CHAPTER XXI. 

 THE SKELETON OF THE DOG 1 (Canis familiaris). 



I. EXOSKELETON. 



The exoskeleton of the dog includes three sets of structures : 

 1. hairs, 2. claws, 3. teeth. Hairs and claws are epidermal 

 exoskeletal structures, while teeth are partly of dermal, and 

 partly of epidermal origin. 



1. Hairs are delicate epidermal structures which grow 

 imbedded in little pits or follicles in the dermis. Specially 

 large hairs forming the vibrissae or whiskers grow attached 

 to the upper lip. 



2. Claws are horny epidermal sheaths, one of which fits 

 on to the pointed distal phalanx of each digit. They are 

 sharply curved structures, and being in the dog non-retractile, 

 their points are commonly much blunted by friction with the 

 ground. The claws of the pollex, and of the hallux when it is 

 present, however do not meet the ground, and therefore remain 

 comparatively sharp. 



3. Teeth 2 . Although as regards their mode of origin, 

 teeth are purely exoskeletal or tegumentary structures, they 



1 W. Ellenberger and H. Baum, Anatomic des Hundes, Berlin, 1891. 



2 T. H. Huxley, "Dental and cranial characters of the Canidae," 

 P. Z. S. 1880. 



