88 Animal Morphology. 



and modes of distribution, yet they are always in pairs 

 or symmetrical. 



The lactiferous tubes are inflections of mucous membrane, 

 and the teats or nipples are supplied with a greater or less 

 amount of erectile tissue. 



The difficulty is to discover where its duplicate serous 

 and muscular membranes lie ; for, however displaced, the 

 distinct membranes may be found, in some form or other, 

 in some near or distinct locality. 



Taking, then, the cervical fascia, which is but condensed 

 connective tissue, it is found that this fascia spreads over 

 and under the clavicle or subdermal ossified membrane, and 

 thence it extends towards the mammary region. Also the 

 same fascia dips down, and, running along the course of 

 the large vessels proceeding from the heart, expands itself 

 and envelopes the heart, where it constitutes the fibrous 

 membrane of the pericardium, within which is enclosed the 

 serous membrane of the pericardium. 



This serous membrane is evidently in co-relation with the 

 primary cervical fascia. 



The heart itself, where it is double, is, correctly speaking^ 

 a symmetrical organ, but for obvious mechanical purposes 

 is lodged in one cavity of the chest, (not necessarily the 

 left) ; for if central the hard and projecting surfaces of the 

 vertebrae would be decidedly objectionable to the freedom 

 of its action, whilst its receiving fascia from either side the 

 cervical region is suggestive of its equilateral origin. 



As the fibrous coat of the pericardium by its origin pro- 

 ceeds from the cervical region, and is therefore an essentially 

 external or subdermal membrane, so the contained serous 

 membrane, with its accompanying fibrous membrane, must 

 also be a subdermal membrane. 



But in its symmetrical relations, as being the enclosed 

 sac protected by the fibrous sheath proceeding from the 



