18 ANATOMY OF VERTEBRATES. 



the scapula, acts through its length with great power upon the 

 well-developed humeral ridge. The f teres major,' /, commencing 

 at the thickened base of the scapula, and deriving fibres from the 

 lower facet of that triedral bone, combines to be inserted into the 

 humerus with part of the latissimus dorsi, m ; a strip from which 

 muscle is extended to the olecranon. The triceps, o, arising 

 from both scapula and humerus, is extremely broad and thick, 

 calling for an extended olecranon for adequate insertion. Part 

 of the powerful flexors of the hand (Jl. digitorum, q, fi. carpi 

 ulnaris, r), and part of the extensors, t, are shown in this view. 

 The pectoralis consists of five thick fasciculi, four of which rise 

 from the sternum, and one from the clavicle : they converge to be 

 implanted into the great 4 humeral ( crista pectoralis : ' to these is 

 added a fasciculus of which the homologue may be traced in 

 Cetacea and Ungulata, passing transversely from one insertion of 

 the pectoral to the other, and serving to combine both trowels in 

 vigorous fossorial action. Of the muscles of the jaws the ( tem- 

 poralis ' is shown at b, and the * masseter ' at c. 



The Hedgehog (Erinaceus) manoeuvres its armour of spines by 

 means of powerfully developed and specially arranged cutaneous 

 muscles. By putting any part of the integument on the stretch, 

 the spines are erected, and their points held firm against the 

 assailant : by the same act of stretching the skin, the proportion 



Dermal muscles of the Hedgehog, xliii. 



thereof to which the prickly armour is restricted can be drawn over 

 ihe whole of the exposed surface of the animal, which in this act 

 rolls and squeezes itself into the shape of a ball. In fig. 7, the 

 Hedgehog is dissected as in the ordinary posture, or unrolled. 

 The layer of muscle, a, a', a f , consists of concentric fasciculi, 

 thin over the middle of the back, a, and becoming thicker 

 toward the periphery, a', a! , which is well defined. All the 



