In the present study, the skull of mithun was roughly triangular (Fig 1) from the dorsal side as reported earlier in chital (
Ramswarup, 2011) and goat of Mizoram
(Choudhary et al., 2020); however, it was pyramidal in ox (
Raghavan, 1964) and elongated in kagani goat (
Sarma, 2006), blackbuck (
Choudhary and Singh, 2016) and chinkara
(Din et al., 2020). The cranial and facial bones were the skull’s major components, with a total of thirty-two bones. There were three single and four paired cranial bones with a total of eleven bones. There was one single and the rest were paired facial bones with a total of twenty-one bones. The cranial bones were occipital, parietal, interparietal, sphenoid, ethmoid, frontal and temporal. The facial bones were maxilla, premaxilla (incisive), palatine, pterygoid, nasal, lacrimal, zygomatic (malar), vomer, turbinate, mandible and hyoid as reported earlier in ox (
Raghavan, 1964), dog
(Miller et al., 1964), ruminants (
Sisson, 1975), horse (
Getty, 1975), savannah buffalo (
Hornsveld, 2002), chital (
Parmar and Shrivastava, 2003;
Kumawat et al., 2014) and blackbuck (
Choudhary and Singh, 2016).
The dorsal surface (Fig 1) of the skull of mithun was formed by the frontal, nasal and incisive bones. In contrast, it was formed by occipital, parietal, interparietal, frontal, nasal and incisive bones in kagani goat (
Sarma, 2006) and chital (
Ramswarup, 2011) and formed by frontal, parietal, nasal and incisive bones in chinkara
(Din et al., 2020). The dorsal surface of the skull of the mithun was extensive in its caudal third. The greatest width of the dorsal surface was noticed at the level of the dorso-caudal margin of the orbital rim.
The frontal bone was irregularly quadrilateral in shape and extensive in mithun as also reported earlier in ox (
Raghavan, 1964) and yak
(Archana et al., 1998a). The frontal bone presented an undulated surface with a distinct interfrontal suture. The cornual processes emerged from the caudolateral angle of the frontal bone with a broad base. They were caudolaterally directed and terminated to a tapering end. The cornual processes were slender in diameter and oriented in a dorso-caudal fashion in ox (
Raghavan, 1964). The intercornual protuberance was less developed and located caudally between the cornual processes in the Indian mithun. In contrast, the intercornual protuberance was more developed in ox (
Getty, 1975) and absent in yak
(Archana et al., 1998a). The supraorbital foramen was a small opening placed slightly caudal to the caudal margin of the orbital rim on the obliquely oriented supraorbital groove (Fig 1); however, the same foramen was situated in the supraorbital groove near to the medial margin of the orbit in ox (
Raghavan, 1964); chital (
Ramswarup, 2011) and blackbuck (
Choudhary and Singh, 2016), whereas it was located within the orbital portion of the frontal bone in bovine (
Diesem, 1968); in the supraorbital groove of the medial brim of the orbit in chinkara
(Din et al., 2019); in the middle to the median margin of the orbital rim in chital (
Parmar and Shrivastava, 2003).
Singh and Patel (1964) also mentioned that the supraorbital foramen was closer to the orbital margin than to the median line (interfrontal suture). In another study, the supraorbital foramen was a huge opening in the blackbuck (
Choudhary and Singh, 2016).
The nasal bone formed the greater part of the roof of the nasal cavity, which was also reported in ox (
Raghavan, 1964) and tiger (
Joshi, 2004). The nasal bone in the present study was articulated cranially with incisive bone and caudally with the frontal bone as reported earlier in blackbuck (
Choudhary and Singh, 2016). The nasal bone was inserted into the frontal bone as a loose attachment as stated earlier in horse (
Getty, 1975), chital
(Kumawat et al., 2014) and blackbuck (
Choudhary and Singh, 2016); however same attachment was closely adherent in ox (
Raghavan, 1964) and sambar deer
(Archana et al., 2003).
The ventral surface (Fig 2) of the skull of mithun can be divided into cranial, choanal and palatine regions. The basioccipital bone in mithun was shorter as compared to that of ox (
Raghavan, 1964). The muscular tubercles were seen to be less developed and widely placed in mithun. The tympanic bulla was small, laterally compressed and less prominent in mithun as also reported in kagani goat (
Sarma, 2006) and Mehraban sheep
(Karimi et al., 2011). In contrast, the same was large in ox (
Raghavan, 1964) and chital (
Ramswarup, 2011). The articular area for the mandibular condyle was found to be wide and flattened in outline in mithun. The placement of the ovale foramen, orbitorotundum foramen and ethmoidal foramen in mithun was similar to the findings in ox (
Raghavan, 1964) and blackbuck (
Choudhary and Singh, 2016).
The palatine region was wide and concave in mithun as reported earlier in ox (
Getty, 1975). The palatine region was formed by the palatine process of the incisive bone, the maxilla and horizontal plates of palatine bones and was circumscribed laterally by the alveolar parts of the maxilla as reported earlier in ox (
Raghavan, 1964). The major palatine foramina (Fig 4) were placed close to the transversepalatine suture in mithun as reported earlier in blackbuck (
Choudhary and Singh, 2016). The palatine fissure and interincisive canal were similar to that of ox (
Getty, 1975). However, the body of the incisive bone (Fig 4) was found to be more flattened in mithun. The maxilla and palatine bones presented eight alveoli for cheek teeth as earlier described in ox, sheep (
Getty, 1975) and yak
(Archana et al., 1998a).
The nuchal surface of the skull was formed by the occipital bone as also reported earlier in camel (
Shahid and Kausar, 2005), blackbuck (
Choudhary and Singh, 2016) and Bardhoka autochthonous sheep breed (
Gündemir et al., 2020). The placement of occipital bone in mithun resembled that of horse (
Getty, 1975), camel (
Singh, 1984), dog
(Miller et al., 1964), chital (
Ramswarup, 2011) and blackbuck (
Choudhary and Singh, 2016). The nuchal surface in the skull of mithun was constricted in the middle due to the well developed temporal fossa. This surface was more extensive dorsoventrally as compared to ox (
Raghvan, 1964) and formed mostly by the squamous and lateral parts of the occipital bone. The external occipital protuberance (Fig 5) was pointed and well developed; however, it was in the form of a thin prominent crest in Binturong
(Kalita et al., 2020). The mastoid foramina were paired and located at the junction between the occipital and parietal bones as mentioned earlier in ox (
Raghavan, 1964) and blackbuck (
Choudhary and Singh, 2016). The occipital condyles were present on the lateral parts of the occipital bone on either side of the foramen magnum as reported previously in blackbuck (
Choudhary and Singh, 2016) and local mizo pig
(Choudhary et al., 2019). The foramen magnum was large and roughly oval in shape as reported earlier in ox (
Raghavan, 1964), chital (
Ramswarup, 2011), blackbuck (
Choudhary and Singh, 2016), chinkara
(Din et al., 2019), goat of Mizoram
(Choudhary et al., 2020) and Bardhoka autochthonous sheep (
Gündemir et al., 2020).
The lateral surface can be divided into cranial and maxillary parts; however, they were continuous without any distinct demarcation in Indian mithun. The lateral surface of the cranial part of the skull of mithun presented a dorsoventrally flattened deep temporal fossa, which waswider in ox (
Raghavan, 1964), shallow and elongated in goat (
Borthakur, 1990), deep but short in yak
(Archana et al., 1998a). The zygomatic arch was massive in mithun. About four or five foramina connecting the temporal canal were present in the caudomedial surface of the temporal fossa in mithun and the same numbers of foramina were located on the ventral surface of the temporal fossa in ox
(Nickel et al., 1981). The axis of the orbit taken from the optic foramen to the middle of the inlet was directed rostral, lateral and slightly dorsal in mithun like in ox as reported by
Diesem (1968). The orbit was formed by the lacrimal, orbital plate of the frontal, supraorbital process, the orbital wing of the sphenoid and the zygomatic bones. The orbital rim (Fig 3) was a thin, rounded margin, smooth in mithun as in yak
(Archana et al., 1998a) and goat of Mizoram
(Choudhary et al., 2018a), whereas it was elliptical in bovine
(Rao et al., 1968) and Mehraban sheep
(Karimi et al., 2011); nearly circular in chinkara
(Din et al., 2019).
The maxillary region was formed chiefly by the maxilla bone and also by the facial parts of the lacrimal and zygomatic bones. The facial tuberosity (Fig 3) was placed above the third superior premolar tooth as reported earlier in ox (
Ghosh, 2012), chital
(Kumawat et al., 2014), blackbuck (
Choudhary and Singh, 2015) and goat of Mizoram
(Choudhary et al., 2020). However, the facial tuberosity was placed at the junction of the fourth and fifth cheek teeth in Kagani goat (
Sarma, 2006); prominent and placed at the level of fifth cheek tooth in Mehraban sheep
(Karimi et al., 2011), Madras red sheep
(Sundaram et al., 2019) and at the superior first molar tooth in Bardhoka autochthonous sheep breed (
Gündemir et al., 2020). The infraorbital foramen was located at the level of the superior first premolar tooth, similar to the findings in chital (
Parmar and Shrivastava, 2003); however, it was situated above the third cheek tooth in dogs
(Nickel et al., 1973), above the level of second check tooth in camel (
Smuts and Bezuidenhout, 1987). As reported in chinkara
(Din et al., 2019), the infraorbital foramen was located at the level of the second cheek tooth; however, in goat of Mizoram
(Choudhary et al., 2020), it was situated dorsally to the junction of the first and second superior premolar teeth.
The mandible (Fig 5) was the heaviest bone of the skull and both the mandibles remained unossified as also reported in spotted deer
(Kumawat et al., 2014) and blackbuck
(Choudhary et al., 2015); however, the mandibular symphysis was ossified in the camel
(Choudhary et al., 2016), horse (
Getty, 1975) and pig
(Choudhary et al., 2019). The body of the mandible consisted of the rostral part and caudal part. The rostral part of the mandible contained the incisor teeth, while the caudal part consisted of the cheek teeth (Fig 5). In the present study, the cheek teeth were three on either mandible
i.e., inferior incisor I, II, III as also reported previously in sambar and barking deer
(Keneisenuo et al., 2020). The cheek teeth were six on either mandible
i.e., three premolar teeth and three molar teeth as also reported in chital (
Ramswarup, 2011), blackbuck
(Choudhary et al., 2015), sambar and barking deer
(Keneisenuo et al., 2020). The canine tooth was absent in the present study. The mandibular tuberosity was very prominent as reported earlier in spotted deer
(Kumawat et al., 2014); however, the mandibular tuberosity was in the form of a tubercle in camel (
Singh, 1984), but it was well developed in yak
(Archana et al., 1998b) and it was not observed in blackbuck
(Choudhary et al., 2015). The body of the mandible (Fig 6) contained the mandibular canal as earlier reported in ox (
Raghavan, 1964), yak
(Archana et al., 1998b), rhinoceros
(Bordoloi et al., 1995), chital (
Ramswarup, 2011) and blackbuck
(Choudhary et al., 2015) for the passage of the mandibular artery, vein and mandibular alveolar nerve. The mandibular canal had its caudal opening mandibular foramen on the medial surface of the mandible and rostrally, the mandibular canal ended with an opening as mental foramen ventral to the diastema.