FORE-LIMB. 117 



their insertion on the side scales 2 or 3 rows behind ; they 

 tend to erect the free edge of the ventral shields. 



Superficial to these muscles lie a series of more or less 

 longitudinal muscles passing from shield to shield, they drag 

 the scales individually forward, sliding one over the other. 

 This action brings the free edges of the shields flat against 

 the body. 0. C. 63 M. 



C. 121. Posterior extremity of the tail of a Spider Monkey 

 (Ateles sp.). The skin has been removed from the dorsal 

 surface to show the mode of attachment of the tendons to 

 the ventral skin. 0. C. 64 M b b. 



Fore-limb. 



C. 122. Right pectoral fin of a Dog-fish (Set/Ilium catulus). 

 Several fairly distinct off-shoots from the trunk-muscles 

 enter into direct relations with the shoulder-girdle and fore- 

 shadow the trapezius, latissimus dorsi, and pectoral muscles 

 of higher vetebrates. The limb-muscles are in the form of 

 simple dorsal and ventral sheets, separable towards the base 

 of the fin into superficial and deep layers, both are inserted 

 into the horny fin -rays. The transition from trunk- to 

 limb-muscles is well shown. 



Humphry, Jour. Anat. & Physiol., vol. vi. 1872, p. 271. 



C. 123. Longitudinal section through the left pectoral fin of a 

 Dog-fish (Scyllium catulus}, showing the arrangement of 

 deep (basio-radial) and superficial layers of muscle on either 

 surface of the fin. 



C. 124. Right pectoral fin of a Sea-Oat (Chim&ra monstrosa). 

 The muscles in connection with the shoulder-girdle are more 

 numerous and show greater individuality than in the Dog- 

 fish. Those proper to the fin are still comparatively simple 

 the superficial and deep layers being clearly defined only 

 on the ventral aspect. Upon the dorsal surface the general 

 muscle-mass, owing to the normally rotated position of the 

 fin, is so folded upon itself that its posterior part runs diagon- 

 ally from the base of the scapula to the posterior margin of 



