110 REPORT 1877. 



muscle ; (2) an anterior deep band of muscular fibres ; (3) a posterior deep muscle, 

 which, according to Professor Macalister, is tbe representative of the pectoralis 

 minor ; and (4) a pectoralis quartus. 



Of tbese the first two are simply constituent parts of tbe great pectoral muscle. 

 Together tbey represent tbe pectorabs major. Tbe superficial part arises from tbe 

 ■whole length of the sternum and ensiform cartilage, and is inserted into the outer 

 lip of the bicipital groove, fusing sbgbtly -with the clavicular deltoid. The deep 

 part of the pectorabs major arises from the anterior third of the sternum, and is 

 quite separate throughout its whole extent from tbe preceding muscle. Stretching 

 outwards as a thick fleshy band, it is inserted into the external tuberosity and 

 outer bicipital ridge. 



Tbe pectoralis minor arises from the posterior two thirds of the sternum, ex- 

 cluding the ensiform cartilage, and also from one or two of the costal cartilages. 

 From this it extends outwards and forwards under the deep portion of the pectora- 

 lis major, and it is inserted into the inner margin of tbe great tuberosity of the 

 humerus, and through the medium of fascia into the tendon of the supraspinatus 

 muscle and the coracoid process. 



Tbe pectoralis quartus (of Macalister) arises from tbe linea alba and from the 

 fascia over the rectus behind the ensiform cartilage, and it proceeds forwards under 

 cover of the superficial pectoral muscle to its insertion into tbe upper part of the 

 pectoral ridge. 



Phascogale. — Tbe pectoral muscles are identical with those of tbe discus with 

 two exceptions, viz. (1) there is no deep muscle corresponding with the deep part 

 of the pectoralis major ; (2) tbe pectoralis quartus is better developed and more in 

 tbe form of a fleshy band. 



In the Tliylacine the pectoral muscles are reduced to a superficial and a deep 

 muscle and a very rudimentary pectoralis quartus. 



The superficial muscle is the representative of the pectorabs major, and arises 

 from that part of tbe sternum which lies anterior to the second costal cartilage. 



The deep pectoral, which represents that muscle to which in the Cuscus we 

 have given the name of pectoralis minor, arises from the whole length of the ster- 

 num behind tbe origin of the preceding muscle, and also from some of the posterior 

 costal cartilages. 



The pectoralis major is inserted into the pectoral ridge at a lower level than the 

 pectoralis minor, which is inserted into tbe outer tuberosity of tbe humerus and 

 into the tendon of the supraspinatus. 



Tbe pectorabs quartus is represented by tbe minute slips of muscle wbich end 

 on the under surface of the pectoralis major. 



On the Brachial Plexus of the Cuscus. By D. J. Cunningham, M.D., 

 Senior Demonstrator of Anatomy, University of Edinburgh. 



In tbe Cuscus the brachial plexus is formed by the anterior divisions of tbe 5th, 

 Gth, 7th, and 8th cervical nerves, together with tbe anterior division of the 1st 

 dorsal nerve. Tbese enter tbe axilla as from cords, tbe 5th and Gth cervical nerves 

 having previously effected a junction. Here they all unite to form a short flattened 

 nervous band, which bes between the axillary artery and vein. 



Branches. — The branches of tbe brachial nerves may be divided into two sets: — 

 1, those which spring from the cords before they enter the flattened band or 

 plexus ; 2, those which arise directly from the plexus. 



Under the first heading we have the suprascapular nerve, the subscapular nerves, 

 tbe musculo-spiral nerve, and the circumflex nerve. 



Of these the circumflex alone deserves special notice, and this on account of the 

 large size and extensive distribution of its cutaneous branch. Under cover of the 

 deltoid muscle it divides into two divisions of equal size ; of these, one suppbes tbe 

 deltoid and teres minor, whilst the other becomes superficial and gives branches not 

 only to tbe skin on tbe outer aspect of the upper arm, but also to tbe skin on tbe 

 outer aspect of the forearm. It apparently talies the place of the cutaneous portion 

 of the nerve which corresponds to the musculocutaneous in man. 



The branches arising directly from the plexus are tbe median, musculocutaneous, 



