Gross anatomical study on bones of pectoral girdle in black swan (Cygnus atratus)

Introduction

The black swan (Cygnus atratus) is a large water bird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. It was introduced to various countries as an ornamental bird in the 1800s. They are black-feathered birds, with white flight feathers. The bill is bright red, with a pale bar and tip; and legs and feet are greyishblack. The pectoral girdle of black swan consists of scapula, clavicle and coracoid.

Materials and Methods

The gross anatomical study was conducted on six adult black swans procured from the postmortem laboratory of Department of Veterinary Pathology, College of Veterinary Science, Rajendranagar, Hyderabad. Wet method of maceration technique was used to separate the bones of pectoral girdle from the remaining body portion of the black swan. The bones of pectoral girdle were cleaned and utilized to observe the gross anatomical features.

Results and Discussion

The pectoral girdle forms the connection between the trunk and the forelimbs. The skeleton of the pectoral girdle consisted of fused clavicles (furcula), coracoid and the scapula as reported by Nickel et al. (1977) [6] and Dyce et al. (2010) [2] in domestic birds. The scapula was a sword shaped bone positioned lateral and parallel to the vertebral column and extended caudally to the pelvis (Fig. 1). It consisted of two surfaces viz., a costal surface and a dorsolateral surface. Both surfaces were convex cranially and caudally showed slight concave dorsolateral surface and nearly flat costal surface with blunt end. The cranial extremity consisted of lateral articular facet for articulation with the head of the humerus, furcular process and a medial rounded process for articulation with the coracoid as observed by Parvez et al. (2016) [7] in pigeon. The scapula joined with the clavicle craniomedially. A neck separated the cranial extremity from the body of the scapula. The clavicle was in the form of thick sickle shaped bone (Fig. 2). These observations were in line with the findings of Chaurasia et al. (2018) [1] in domestic ducks whereas Nickle et al. (1977) [6] observed thin and slightly curved branches of clavicles in fowl and pigeon. A pair of clavicles fused ventrally to form a broad'U' shaped furcula similar observations were [5] in green-winged macaw, Shabir et al. (2013) [9] in the domestic geese and Parvez et al. (2016) [7] in pigeon. The hypocledium was absent as observed by Indu et al. (2012) [5] in green-winged macaws whereas in crow the hypocleideum was in the form of flattened 'S' shaped sagittal plate as observed by Patki et al. 2010 [8] and in fowl it is in form of an oval thin plate (Getty, 1975) [4] . A lateral ridge was prominent throughout the length of furcular branches similar observations was made by Nickle et al. (1977) [6] and Chaurasia et al. (2018) [1] in domestic ducks. The proximal end of the clavicle had facet for coracoid as observed by Parvez et al. (2016) [7] in pigeon whereas in the domestic geese the proximal extremity had no facet but only a rough area for coracoid as observed by Shabir et al. (2013) [9] . The proximal ends of clavicle, coracoid and scapula articulated to form foramen triosseum similar observations were made by Nickle et al. (1977) [6] in fowl and Shabir et al. (2013) [9] in domestic geese. The coracoid was a thick rod-shaped and strongest bone of the pectoral girdle which was directed downward and backwards. It consisted of two extremities and a shaft (Fig. 3). The cranial extremity was narrower than caudal extremity. The cranial extremity was characterized by the presence of humeral, scapular, acrocoracoid tuberosities and a shallow supracoracoid groove. The acrocoracoid process of coracoid bone was tuberous and presented a small pneumatic foramen medially however, coracoid bone of pigeon and owl lacked this foramen. The caudal extremity was quadrilateral and consisted of spatula shaped concave elongated facet crest to articulate with the sternum and few rough lines similar observations et al. reported were made by El-Ghazali et al. (2023) [3] in domestic ducks.

Acknowledgement

We sincerely thank department of Veterinary Anatomy, C.V.Sc Rajendranagar, Hyderabad for having provided the necessary facilities for carrying out this work.

References

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