Animal Morphology. 89 



cervical fascia, its primary seat or origin is from the fascia 

 on either side the neck ; and had the rudimentary ribs or 

 true haemal arches in the cervical region been fully developed, 

 we might have had the mammas in the neck and the serous 

 membrane, enveloped by a strong fibrous sheath, in one or 

 more detached positions, according to the site and position 

 of the mammary distribution, and the heart altogether 

 differently arrranged, but within the cervical haemal 

 arches. 



But as it now is, the mammary glands, saving their being 

 placed somewhere in the anterior aspect of the haemal 

 arches, have no fixed form of distribution. Ruminants 

 have one locality, canine another, pachydermata a some- 

 what roving order of distribution, and man another. So, 

 in the displacement of their serous membrane, though 

 constancy is observed, yet it is far removed from the 

 seat of its original place of distribution. 



This singular membrane is essentially a subdermoid tri- 

 partite membrane, and carries with it a singular differentia- 

 tion in its contractile membrane. This membrane, being 

 outside the neural and haemal arches, demands new func- 

 tions, and partakes of a new form of differentiation in the 

 form of striped muscle, and the Plafysma is probably 

 the simplest form of a true subdermal muscle in man, and 

 is the true contractile membrane of the tripartite mammary 

 membrane. 



The mammary tripartite membrane is interesting upon 

 another score than that which, as it were, introduces us to 

 a morphology and differentiation in cell development most 

 extensively used in the animal kingdom namely, the striped 

 muscular membrane. 



For this membrane namely, the mammary membrane 

 appears to be the last membrane added to the vertebrata, which 

 introduces us into the highest class of animals ; and its classi- 



