CHAPTER 3 

 ANATOMY 



1. Anatomy (gross and microscopic). 2. Embryology. 3. Bones Connec- 

 tive tissue. 4. Muscles. 5. Blood vessels and lymphatics. 6. Nervous sys- 

 tem. 7. Sense organs. 8. Integument. 9. Thoracic and abdominal viscera. 

 10. Uro-Genital system. 11. Exocrine glands. 12. Endocrine system. 



Since it is our purpose to present mainly those results that 

 are quantitative, there will appear several divisions of this 

 chapter marked only by references to the literature. 



Further, even in those divisions for which there are some 

 available data it happens in many cases that the presentation 

 of them can be better given in the chapters which treat of growth, 

 and in such instances the reader is merely referred to the latter 

 place of presentation. These general statements apply to the 

 subsequent chapters as well. 



1. Anatomy. In only two instances has the rat been used 

 as the basis for a general presentation of mammalian anatomy. 

 These are in the books by Martin and Moale, 1884, and Goto. 

 1906. The remaining references are to studies which apply to 

 portions or systems only (see classified references at the end 

 of the chapter). 



2. Embryology: (a) Spermatogenesis. According to Hewer 

 ('14): 



In the newborn animal, active mitosis is occurring in the testis, and at 

 3| weeks the spennatogonia can be distinguished from the spermato- 

 cytes. No lumen begins to appear in the tubules as a rule until 7 weeks. 

 At 8 weeks spermatids are easily distinguishable. At 9 weeks typical 

 ripe spermatozoa are plentiful, but the fully formed epididymis con- 

 tains no free spermatozoa. At 10 weeks all the tubules show active 

 spermatogenesis: the second crop of spermatozoa is appearing, while 

 the first crop can be seen in the epididymis. 



Using rats from the Institute colony Allen ('18) finds that 

 the first spermatocyte cells begin to differentiate between the 

 seventh and tenth days after birth and that the first spermatozoa 



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