PROFESSOR TURNER ON THE PLACENTATION OF THE SLOTHS. 103 
the mammalian series, and the use of this organ as a basis of classification, 
though in many instances it may be relied on, yet, from the complex cross 
relations which exist between the several organic systems in the placental 
mammals, is not universally applicable. 

This woodcut is a diagrammatic representation of the advanced ovum of 
Cholepus Hoffmanni. The shaded part (PJ) shows the proportion of chorion 
on which the placenta is developed. Chis the non-placental area of the 
chorion. The dotted line (am) the amnion. w, the umbilical cord. Lp, 
the epitrichium investing the fcetus. 
EXPLANATION OF PLATES. 
Figures 1, 2, and 3 were drawn from nature, under my superintendence, by Mr Joun Rep; and 
figures 4, 5, 6, 10, and 11, by Mr C. Berszav. Figures 7, 8, 9, are from sketches made with the 
camera lucida, by myself. : 
Puate III. 
Figure 1. Posterior surface of the gravid uterus of Cholcepus Hoffmanni. The rectum is drawn to one 
side ; the anus and external opening of the genital passage are surrounded by a common 
fringe of hairs. Reduced about 4d. 
Figure 2 represents a portion of the placenta dissected off the surface of the uterus, to show the curling 
arteries, utero-placental veins, deciduous and non-deciduous serotina. Ut, uterus; P/., pla- 
centa; ¢ ¢’, curling artery, torn through in separating the placenta from the uterus; v », 
utero-placental veins ; 7 Ss, non-deciduous serotina ; @ s, deciduous serotina, thin flakes of 
which are shown passing between the uterine and placental surfaces. At c’ and v’ the non- 
deciduous serotina has been dissected off, and the muscular coat, with its nutrient blood- 
vessels, exposed. Magnified about 4d. 
Puate LV. 
Figure 3. The interior of the cavity of the uterus, with the placenta 7 situ, the umbilical cord, foetus, 
and epitrichium. The uterus has been opened into by a median longitudinal incision through 
its posterior wall. The inner surface of the placenta, displaying its lobes and the ramifi- 
VOL, XXVII. PART I. 2D 

