262 MB. F. G. PARSONS ON THE [Mar. 20, 



comes from the spine of the scapula and fascia over the infra- 

 spinatus. Mivart and Murie, in their description of the myology 

 of the Agouti ', prefer to describe the clavicular portion as part of 

 the pectoralis, but I have been able to satisfy myself that its nerve- 

 supply is derived from the circumflex and not the anterior thoracic. 

 The insertion of the deltoid is into the pectoral ridge close to that 

 of the pectoralis. The clavicular fibres are often prolonged to the 

 elbow and in all cases are inserted lowest, while the part from the 

 spine is inserted deep to the acromial slip. 



In the Dasyproctidse the clavicular portion is continued down 

 almost to the external condyle. 



In Sciurus and Pteromys the clavicular and acromial fibres are 

 closely united owing to the development of the clavicle. Sphin- 

 yurus has the same arrangement. 



In Arctomys and Spermophilus the clavicular part divides into a 

 superficial and deep portion ; the latter has the usual insertion, but 

 the former is continued down to the coronoid process of the ulna. 

 In Castor, owing to the great development of the muscle, the 

 intervals between the three parts are slight. The other animals 

 examined present nothing remarkable iu this muscle. 



Supraspinatus, Infraspinatus, and Subscapularis. — These muscles 

 have the human attachments and, except in their comparative 

 size, do not vary at all. 



Teres Major. — This muscle rises from the posterior quarter 

 (more or less) of the axillary border of the scapula, and is inserted 

 either into the tendon of the latissimus dorsi or into the humerus 

 close to the insertion of that muscle. 



In the Dipodida? the insertion is posterior to that of the latis- 

 simus dorsi as in Man (D. cegyptivs, I), hirtipes, Alectaya inclica). 



In the Octodontidse it is inserted into the front of the tendon 

 of latissimus dorsi (Aulacodus, Myopotamus, Octodon, Capromys 

 pilorides and C. melanurvs) \ 



In Layostomus among the Chinchillidse, owing to the great 

 size of the infraspinatus, the muscle only rises from about gth of 

 the axillary border of the scapula and from the surface of the infra- 

 spinatus and subscapularis, which overlap the bone. The insertion 

 is into the rudimentary bicipital groove somewhat above the 

 latissimus dorsi tendon, with which it is closely connected. 

 Chinchilla has very much the same arrangement, but the muscle 

 rises from more of the axillary border. 



In the Hystricidae the lower border of the muscle is wrapped 

 round by the latissimus dorsi close to the insertion {vide latissimus 

 dorsi) (ifystrix, Sphingurus). 



In the Dasyproctidse it was inserted nearer the shoulder than 

 the latissimus dorsi in my specimen of Dasyprocta, but according 

 to Mivart and Murie 3 the two muscles are inserted together. In 

 Ccelogenys it is inserted with, and in front of, the latissimus dorsi. 



1 P. Z. S. 1866, p. 383. 



2 Dobson, P. Z. S. 1884, p. 234. 



3 P. Z. S. 1866, p. 383. 



