(JS(3 MBSS5J{S. U. C. A.. WINJJLE AND J;'. C4. PA11.SONS ON | Dec. 17, 



sheets, a superficial and a deep, but the subdivisions ot; these vary 

 immensely, and it would hs impossible to quote all the combinations 

 M'hicli are described, nor do we think it desirable to do so as the 

 arrangements are not even constant for the same animal. 



The superficial sheet rises from the pre- and mesosternum, and 

 usually consists of a main quadrilateral part which is inserted 

 into the pectoral ridge and greater part of the shaft of the hiimerus ; 

 in addition to this there is usually an insertion into the fascia of 

 the forearm near the elbow which rises from tlie mesosternum 

 behind the last but in many cases overlaps or is overlapped 

 by it. 



The oblique superficial band running from the presternum to 

 the lower part of the insertion of the muscle, which is so frequently 

 found in the liodents, seems only to be present in the Procaviidse, 

 where it comes from the cartilaginous omosterfuim and goes to 

 the lower half of the humerus. The deep layer consists of the 

 pectoralis quartus which rises from the posterior part of the meso- 

 sternum and from the linea alba and Mhich runs for\^^ard, 

 narrowing as it goes, to the region of the great tuberosity of the 

 humerus and blending witli the panniculus. Ccphalad of this is 

 often another slip, which is the pectoralis minor of most authors, 

 coming from the mesosternum and being inserted with the last- 

 named into the fascia over the front of the shoulder-capsule. 

 These two deep slips are in the same plane as the sterno-scapular 

 muscle which is often included in their description. 



Eoughly speaking, the pectoral mass of the Ungulates bears out 

 the usual mammalian tendency, which is for the most superficial 

 fibres to be drawn towards the lower i)art of the arm, while the 

 deeper ones concentrate their action on the upper part. The 

 nerve-supply of the pectoralis minor, quartus, and ventral panni- 

 culus is from the great internal anterior thoracic nerve ; the moi'e 

 superficial la}-er is partly supplied by the external anterior tlioracic, 

 l)artly by the internal. There is tlierefore a sharp demarcation in 

 the nerve-supply between the pectoralis. minor and the sterno- 

 scapularis. 



Muscles of the Fore-Umh. 



Deltoid. — Tlie clavicular portion of this muscle has been already 

 described with the cephalo-htiraeralis. The acromial part is usually 

 absent owing to the siippression of the acromion process, but in 

 the Elephant (77, 78, 79), in which the acromion is found, this 

 part of the muscle is well develo])ed and rises from the fork 

 between the two processes. In the Hippopotamus (3) and 

 Tragulus (20, 21) the acromial part is well developed, but in the 

 Tapir (54, 55), although present, it is feebly developed. In the 

 Hyrax (67), Mivart and Murie describe the acromial part as rising 

 J'romthe great tuberosity of the humerus, but in our specimen (68) 

 it was entirely absent. 



The spinous portion is a very thin sheet which rises not only 

 from the spine of the scapula but also from the fascia over the 



