Second Day. 



Skeletal System (Part). 



1. Remove the pectoralis muscles covering the body between the arms 

 to show the bones of the central part of the shoulder girdle and sternum, 

 viz. : — 



(a) The thick coracoids. 



(b) The more slender clavicles anterior to them, both extending from 



the base of the arm on each side towards the centre of the body. 



(c) The sternum, consisting of a median row of cartilages which are 



believed to be derived from the shoulder girdle. It does not, there- 

 fore, correspond to, or is not homologous with, the sternum of the 

 Pigeon or the Rabbit, which is derived from the ribs. The sternum 

 consists of the following parts : 



(i) The two epicoracoids consisting of cartilage. 



(ii) The metasternum which is broad and consists of cartilage only. 



osternum 



trnum 



Epicoracoid 



Coracoid 



Epicoracoid 



Sternum 



Xiphisternum 



Fig. 4. — Pectoral Girdle of Xenopus and Rana. 



[In the Frog the sternum is composed of the following parts : — ■ 



(i) The omosternum consisting of tivo parts, an anterior cartilaginous 

 part (sometimes called the omosternum) and a posterior bony part 

 (sometimes called the episternum). 



(ii) The two epicoracoids consisting of cartilage, 



(Hi) The metasternum consisting of two parts, an anterior bony part 

 (sometimes called the sternum) and a posterior cartilaginous part 

 (sometimes called the xiphisternum).'] 



Make a sketch of the pectoral girdle. 



10 



