The sternum of the Asian koel was a large, quadrilateral shaped bone, concave dorsally and convex ventrally (Fig 1). It weighed 41 mg and consisted of a manubrium sterni or sterna spine, body or corpus sterni (Fig 1) and a keel or sternal crest (Fig 2). The sternal spine was present at the middle of the cranial border of corpus sterni arose from both the dorsal and ventral edges of the groove. It was about 4mm long, quadrilateral, flattened plate of bone with rounded tip, projecting straight cranially (Fig 3).
Dursun et al., (2002) reported that, the sternal spine was approximately 3 mm in height, 5.5 mm in length and 1.5 mm in thickness, in bald ibises.
Nickel et al., (1977) observed that in fowl, the sternal spine arose as two processes from the dorsal and ventral edges of the groove, which fused into a median vertical bony plate, leaving an opening between them. In pigeon, the two processes remained separate, while in duck and goose, only the ventral process was present. In spot-billed pelicans, it extended from the ventral edge only
(Sathyamoorthy et al., 2012). In common myna, Himalayan bulbul and house sparrow, the sternal spine was ‘Y’ shaped
(John et al., 2017). The sternal spine was smaller in crested serpent eagle
(Choudhary et al., 2018), thick, upwardly bent spine-like process and arose only from the ventral edge in blue and yellow macaw (Sathyamoorthy
et al., 2019). In contrary, the sternal spine was absent in black kite
(Tomar et al., 2011).
The corpus sterni was quadrilateral in shape (Fig 1). It was 3.4 cm long and 2.1 cm wide in the centre. It is in agreement with the observations of
Nickel et al., (1977) in duck and goose,
Dursun et al., (2002) in bald ibis,
Tomar et al., (2011) in black kite and
John et al., (2014a) in pigeon hawk.
The dorsal surface was deeply concave in the cranial two thirds and convex in the caudal one third (Fig 1). The ventral surface was convex in the cranial two thirds and concave caudally (Fig 2). These findings were in agreement with the observations of
John et al., (2017) in common myna. The dorsal surface of the corpus sterni showed a groove in the centre. Cranial two-thirds of the groove showed pneumatic foraminae. The cranial most of these foraminae was the largest, extending into the cranial border of the sternal crest. In addition, numerous pneumatic foraminae were also noticed behind the cranial border as well as on the lateral borders in the cranial half of the dorsal surface (Fig 1). It is in agreement with the observations) in bald ibis
(Dursun et al., 2002), pigeon hawk
(John et al., 2014a) and Himalayan bulbul, common myna and house sparrow
(John et al., 2017).
In Asian koel, the cranial border of the sternum was thick and semicircular and presented dorsal and ventral ridges and deep articular grooves on either side for the coracoid bone. The ventral ridge was thicker than the dorsal ridge. The dorsal ridge was continuous with the craniolateral processes (Fig 3), in accordance with the observations of
Nickel et al., (1977) in fowl, pigeon, duck and geese. The cranial border was triangular in black kite
(Tomar et al., 2011), peacock and turkey
(Pathak et al., 2017).
In the present study, the craniolateral processes were well developed, roughly quadrilateral, thin and projected dorsolaterally and cranially. It was about 6 mm long, broad at the base and narrow at the apex. Its borders were thick, while the centre was thin (Fig 1).
Nickel et al., (1977) reported that this process was very large in fowl, very short in pigeon and small in duck and goose. In blue and yellow macaw, the craniolateral processes were very short and roughly quadrilateral
(Sathyamoorthy et al., 2019). This process was short in pigeon hawk
(John et al., 2014a), highly developed in mynah, moderately developed in Himalayan bulbul and least developed in house sparrow
(John et al., 2017).
In the present study, the lateral borders between the craniolateral and caudolateral processes were short, thick and showed four articular cylinders projecting laterally for the articulation with the sternal ribs. Between the articular cylinders, three well defined, deep pneumatic foraminae were present (Fig 1). In green-winged macaw
(Sreeranjini et al., 2015) and in pigeon hawk
(John et al., 2014a) six articular cylinders with troughs containing pneumatic foraminae was noticed. Four pairs of articular cylinders were present in house sparrow, 5 pairs were present in mynah and Himalayan bulbul
(John et al., 2017), spot-billed pelicans (
Sathyamoorthy et al., 2012) and blue and yellow macaw
(Sathyamoorthy et al., 2019) and 4 pairs in turkey, 7 pairs in duck and white-breasted waterhen (
Pathak et al., 2017).
In Asian koel, the caudolateral processes were about 1.0 cm long. At the caudal end the processes were 0.8 cm broad and at the beginning they were 0.45 cm broad. Between the caudolateral process and the corpus sterni a triangular notch, the incisura ovalis was formed. The caudal process did not extend beyond the caudal border of the sternum. Hence, the caudal border of the body of the sternum formed the caudal end of the sternum (Fig 1).
Pathak et al., (2017) reported that, in peacock, turkey and duck, the caudolateral processes did not reach up- to the caudal end of the middle piece of the sternum, but in white-breasted waterhens, they extended beyond the caudal end of the sternum. In common moorhen, the caudolateral processes were long, thin and terminated well behind the caudal end of the sternal body
(Wani et al., 2017).
In Asian koel, between the caudolateral processes and the lateral border of the body a triangular notch, the incisura ovalis was formed (Fig 1).
Nickel et al., (1977) observed that in fowl, the incisura ovalis was elongated. But, in older goose, it was completely encircled to form foramen ovale. In bald ibises, two incisures were noticed at the caudal border
(Dursun et al., 2002). In pigeon
(Nickel et al., 1977), pigeon hawk
(John et al., 2014a), green -winged macaw
(Sreeranjini et al., 2015) and in blue and yellow macaw
(Sathyamoorthy et al., 2019) it fused with the caudal border of the sternum, formed foramen ovale and convex caudal border of the sternum.
In Asian koel, the processes thoracicus was absent as in spot-billed pelican
(Sathyamoorthy et al., 2012), crow and lapwing
(John et al., 2014b), pigeon hawk
(John et al., 2014a) common moorhen
(Wani et al., 2017), duck and white - breasted waterhen
(Pathak et al., 2017), common myna, Himalayan bulbul and house sparrow
(John et al., 2017) and in blue and yellow macaw
(Sathyamoorthy et al., 2019).
In the present study, the caudal border of the sternum was 1.3 cm broad and slightly convex. The caudal border of the sternal body formed the caudal most structure (Fig 1).
Dursun et al., (2002) noticed that in bald ibis, the caudal border contained a strong processes caudolateralis, a small intermediate processes and a large central process. Hence, the caudal border was zigzag.
In Asian koel, the sternal crest was well developed, triangular plate, projected from the ventral surface of the sternum and extended up to the caudal border. It formed a steep caudally directed arch. The cranial border of the sternal crest was concave, sharp, thick dorsally and thin ventrally. Ventrally, it extended beyond the level sternal spine and its tip formed the cranial most part of the sternum (Fig 2). In spot-billed pelicans the sternal crest was triangular, small and extended only up to the cranial half of ventral surface. Its cranial border was straight and sharp and extended beyond the cranial border of the sternum
(Sathyamoorthy et al., 2012).
