Anatomy and Physiology of the Mammary Gland. 83 



intrusion." Thus \ve see that the same laws obtain with regard 

 to these creatures as are in force with reference to terrestrial 

 • dnammals. 



It will be apparent from tlie precedins: remarks that the mam- 

 mary glands belong to the reproductive system, and are to be 

 viewed as most important auxiliaries of the generative organs. 

 Placed as a general rule as much as possible in a situation of 

 security, and one also of easy access to the young animal, these 

 glands will nevertheless be found to vary considerably in their 

 location, and even so among our domesticated animals. In the 

 mare, cow, ewe, and goat, they are situated far back on the under 

 surface of the abdomen — the pubic region of the anatomist, — and 

 are here securely protected from injury on either side by the hind 

 limbs. In the pig, bitch, and cat, on the contrary, they are 

 -arranged in two rows, on either side of the medium line of the 

 abdomen, and extend from the pubic region l^ehind to the pectoral 

 region, or breast, in front. In the human subject it is well known 

 that the mammae occupv the pectoral region, and the same is the 

 <'ase with the quadrumana, also with the elephant, and several other 

 creatures. 



As both secretion and development depend on the freedom 

 <jf the supply of blood to the part, so it is found that in many 

 instances the same organs in animals of different classes obtain 

 their blood from vessels which are identical in their origin 

 with those in creatures from which thev themselves differ. 

 It is evident, however, from the great variation which exists in 

 the position of the mammae among domesticated animals, that 

 these organs not only receive their blood from different vessels, 

 both according and near to tlieir location, but that tliey return 

 also as much of it as is unappropriated back to the heart througli 

 contiguous venous canals, which are unused for such a purpose 

 in other animals. These anatomical facts, although not properly 

 belonging to the subject we have principally to treat of, are never- 

 theless necessaiy to be mentioned for the better elucidation of 

 the peculiarities attaching to the mammary glands of the cow. 



From the foregoing observations it will be inferred that the 

 aiumber of the mammae is subject to great variation. In the 

 mare, the ewe, and the goat, we find two ; in the cow four, or 

 occasionally six, the two additional ones being generally but im- 

 perfectly developed ; in the bitch ten or twelve, and in the pig 

 often as many as sixteen or eighteen. To some extent their num- 

 ber affords an index to the quantity of young animals which may 

 be produced at a birth, but not, we think, sufficiently so for it to 

 constitute a rule. For example, in the selection of multiparous 

 animals for breeding, care is usuallv taken to choose such as 

 possess a large number of mammse ; but how often do we find that 



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