68 THE ROYAL SOCIETY OF CANADA 
5. CaroTip Bopy. 
Anatomy. 
To the unaided eye the carotid body is visible as a marked swelling 
or dilatation in the course of the external carotid artery quite close to 
the bifurcation of the common carotid. (See Pl. VI, fig. 8). 
Histology. 
It is a spongy cavernous body and it is doubtful whether any 
structures other than those of blood vessels enter into it. 
PROPERICARDIAL Bopy. 
Historical. 
According to Gaupp the body was first described by Simon? (1845) 
as the thymus. This author stated that in young animals it “has the 
true structure of the thymus” but in older animals becomes converted 
into fat. In his drawing Gaupp thinks that Simon included not only the 
true corpus propericardiale but also other accumulations of fat in the 
neighbourhood of the pericardium. (See PI. VI, fig. 9). 
Histology. 
The specimen from which (Pl. VI, fig. 9), was drawn was pre- 
sumably an adult, but had a small nodule of adenoid tissue still remain- 
ing. It appears to consist of anirregular elongated nodule of connective 
tissue permeated by blood vessels with masses and columns of leucocytes 
irregularly disposed. As I have not been able to examine the 
body in young specimens it is impossible to offer any further de- 
scription of the microscopic structure. The body is surrounded with 
irregular masses of fat and these indeed constitute all that is visible to 
the unaided eye. 
6. Procoracoip Bopy. 
An account of this body is given by Gaupp, who states that in 
young animals it possesses a lymphoid structure. It appears to be 
developed at an earlier date than the propericardial body. I have 
examined the body only in adult specimens and in these it is made up 
entirely of adipose tissue. 

1 Loc. cit. 
2 A physiological essay on the Thymus Gland, London, 1845. 
