288 



Dr. M. Watson. 



sections were made with the view of determining whether these 

 vessels ever passed beyond the placental substance, in no single 

 instance did I ever detect such an appearance as conld lead me to 

 believe that the vessels in question had been divided, and had, pre- 

 vious to the detachment of the placenta, passed from the latter into 

 the wall of the uterus. Had such a passage taken place, it seems im- 

 probable, in view of the comparatively large size of these vessels, that 

 the torn extremities of some at least of them would not have been 

 recognised. The absence of any such appearance lends support to the 

 view that the vessels under consideration really constituted and 

 belonged to the foetal portion of the placenta. Horizontal sections of 

 the placenta, that is, sections made parallel to the surfaces of the organ, 

 presented a different appearance. In these, by far the greater number 

 of the vessels were seen to be either obliquely or transversely divided. 

 This showed that these transverse anastomosing vessels above de- 

 scribed were not for the most part united at right angles with the 

 vertical trunks with which they inosculated, but that they pursued a 

 more or less oblique course between the latter. Had they passed off at 

 right angles with these, the appearance of the horizontal would have 

 closely resembled the vertical sections, whereas, whilst the latter 

 under the microscope presented a very similar appearance, the hori- 

 zontal sections differed from them in respect of the much smaller 

 number of longitudinally divided vessels which were visible. 



When a portion of the placenta was teased out with needles under the 

 microscope, these vessels were seen to be provided with extremely thick 

 but apparently structureless walls. When immersed in solution of log- 

 wood, the latter were readily stained by that reagent. That they were 

 composed of a form of elastic tissue was clearly shown by the singular 

 immunity which they exhibited to the action of different reagents. 

 Even when boiled in dilute hydrochloric acid, or digested for eighteen 

 hours in solution of caustic potash, the walls of the vessels underwent 

 apparently little change, and subsequently manifested their elastic 

 nature by the resistance which they offered to the pressure of the 

 covering glass. Professor Turner* observes that the walls of vessels, 

 which, in other respects, present so close a resemblance to those under 

 consideration, which he met with in the maternal portion of the 

 placenta of Gholo&pus Hoffmanni, possessed " no elastic tissue or 

 muscular fibre cells." So far as the absence of muscular fibres is con- 

 cerned, the placental vessels of Procyon agree with those of Gholcepus, 

 but differ inasmuch as the wall, although apparently homoge- 

 neous under the microscope, is distinctly elastic in character. These 

 vessels, in Procyon, were provided with a distinct endothelial lining 

 which, although not always distinguishable, was in some vessels 



* " Trans. Roy. Soc. Edin.," vol. xxvii, p. 80. 



