338 SHOULDER-GIRDLE IN MONOTREMES, 



M. SERRATUS MAGNUS. 



Origin. This muscle arises from the first four ribs, the 

 origin from the first rib being placed about '6 cm. from the spinal 

 extremity of the rib, while the origins from the other ribs are 

 placed successively further out. 



Insertion. The four slips are collected into one belly of 

 muscle, which is inserted on to the posterior one-sixth of the 

 vertebral border of the scapula ; the insertion being closely related 

 to, and placed between, the origin of the teres major and scapular 

 part of the latissimus, and the insertion of the posterior portion of 

 the levator scapulae internally. 



Relations. At its origin the muscle is relat' d to the digi- 

 tation of the external oblique, while the slip from the first rib ig 

 related to the costo-coracoideus and scalenu.s. In its course the 

 latissimus dorsi passes superficial to it, and hides it from view. 



M. LEVATOR SCAPUL,*:. 



Or.mthoriiynchus. 



This muscle is divided into two portions, a dorsal stratum, und 

 a ventral stratum. 



Origin, (a) Dorsal portion. — This arises by six digitations 

 from the tips of the transverse processes of six cervical vertebra; 

 (2nd-7th). 



Ins 61 tion. The terete bands run towards the scapula and 

 coalesce to form a single muscle, which is inserted on the posterior 

 half of the inner edge of the vertebral border of the scapula. The 

 bands from the second and third cervical vertebrae are intimately 

 connected with the ventral bauds from these vertebrae, while the 

 bands from the more posterior vertebrae are connected with the 

 serratus magnus. 



Relations. At its insertion the muscle is related to the 

 serratus magnus, rhomboid, acromio-trachelien and to the sub- 

 scapularis. 



Origin, (b) The ventral portio7i arises by five digitations 

 from the transverse processes of five cervical vertebrae (2nd- 6th). 



