37 
IY. — CONTRIBUTIONS TO THE 
HISTOLOGY OF THE THREE-TOED SLOTH 
(BRADYPUS TRIDACTYLUS). 
By Charles F. Sonntag, M.D., F.Z.S., F.R.M.S., Anatomist to 
the Zoological Society of London ; and F. Martin Duncan, 
F.R.P.S., F.Z.S., F.R.M.S. 
(Bead June 15, 1921.) 
Thirteen Text-Figures. 
The materials on which the present paper is based consisted of 
the hairs and tissues of an adult female Bradyjpus tridactylus 
which died in the Zoological Society’s Gardens. The sections 
were prepared by the usual paraffin method, and stained with 
haematoxylin and acid eosin. 
One of us (C. F. S.) has already described the macroscopic 
appearances of the organs.* 
The Tongue (text-fig. 1). 
The histological characters show that the mechanical functions 
predominate over the sensory ones. 
The conical papillae are small and discrete. They have a thick 
epithelial covering which is drawn out into one or more sharp 
points directed backwards and inwards. The fungiform papillae 
are flat, circular and scanty ; they have few taste-buds, but sensory 
nerve-endings are present. The two circumvallate papillae are 
smooth and glistening, and are conical on elevation with the bases 
of the cones projecting beyond the well-marked annular valiums ; 
and they can be powerfully retracted when irritated ; lateral 
organs or foliate papillae are absent. The gustatory organs are, 
therefore, few in numbers. 
Serous and mucous glands are present as usual on the base of 
the tongue, but are not strongly developed, and they are accom- 
panied by a few lymphoid nodules. The diminution in the 
glandular apparatus is in keeping with the reduction in the 
gustatory organs. Ho apical gland of Nuhn is present. 
* “ A Contribution to the Anatomy of the Three-toed Sloth,” Proc. Zool. 
Soc., London, 1921, pp. 157-77. In this paper there are photographs of the 
various parts of the stomach, whose histology is described below. 
