686 U.ESSK8. B. C. A. WJNDLK A MJ 1. G. PARSON'S UN Dee. 17. 



sheets, a, superficial and a deep, but the subdivisions of tbese varj 

 immensely, audit would be impossible to quote all tbe combinations 

 which 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 humerus ; 

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

 the forearm near the elbow which rises from the mesosternum 

 behind the last but iu many cases overlaps or is overlapped 

 by it. 



The oblique superficial band running from tbe presternum to 

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

 found in the Rodents, seems ouly to be present in the Procaviida\ 

 where it comes from the cartilaginous omosternum 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 which runs forward, 

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

 humerus and blending with the panniculus. Cephalad 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 frout of the shoulder-capsule. 

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

 muscle which is often included in their description. 



Roughly 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 part 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 more 

 superficial layer is partly supplied by the external anterior thoracic, 

 partly by the internal. There is therefore a sharp demarcation in 

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

 scapularis. 



Mastics of the Fore-Umb. 



Dcltvld. — The clavicular portion of this muscle has been already 

 described with the cephalo-hunieralis. The acromial part is usualh 

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

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

 part of the muscle is well developed 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 

 from the great tuberosity of the humerus, but in our specimen (68) 

 it was entirely absent. 



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

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



