326 Dr. Watney. Minute Anatomy of the Thymus. [Jan. 20, 



tion, at tlie same time that it differs from those composing both the 

 digitigrade and pinniped sections of the carnivora, inasmuch as at one 

 spot the placenta presents a deficiency or gap, at which spot the pla- 

 cental structure is imperfect. 



(4.) That Procyon agrees with Canis, at the same time that it differs 

 from Felis, in the absence of a continuous layer of decidua serotina from 

 the uterine surface of the detached placenta. 



(5.) That Procyon differs from every other carnivore, the placenta of 

 which has been minutely examined, in the possession of placental 

 vessels possessed of a structure hitherto only met with in the placenta 

 of Choloepus Hoffmanni among the Edentates. 



(6.) That Procyon differs from every other carnivore, the foetus of 

 which has been hitherto examined, in the non-possession of an umbilical 

 vesicle. 



(7.) That Procyon differs from all carnivora of which the young 

 have been hitherto examined, inasmuch as the foetus is provided with a 

 supernumerary cuticle or epitridermia, a structure which has only been 

 met with in the young of certain members of other mammalian groups. 



From an examination of the various facts detailed in the paper, the 

 author arrives at the conclusion that a consideration of the modifi- 

 cations in form and structure of the placenta alone is insufficient as 

 affording a basis upon which to found a natural classification of the 

 mammalia. 



V. "Further Note on the Minute Anatomy of the Thymus" 

 By Herbert Watney, M.A., M.D. Cantab. Communicated 

 by E. A. S chafer, F.R.S. Received January 3, 1881. 



In the involution of the thymus, connective tissue is formed in the 

 medullary portion of the follicle ; and to some extent in the cortical. 

 Besides this, the connective tissue outside the follicles increases, and 

 in this connective tissue fat is formed ; by these means the gland is 

 finally replaced by fat and fibrous threads. 



The cortical part attains its greatest size at the time of the greatest 

 activity of the gland, it is not differentiated from the rest of the 

 follicle at a very early period and disappears somewhat sooner than 

 the medullary portion. 



The lymphatics of the thymus of the calf are small. In the neck 

 they run to neighbouring lymphatic glands, the efferent vessel of 

 which runs to two other lymphatic glands lying on the trachea at the 

 root of the neck. There is no connexion with the large lymphatics 

 of the neck. In the thoracic portion of the thymus the lymphatics 

 can also be traced to lymphatic glands, one of which is generally 

 situated on the aorta. 



