6i 



DR. N. II. ALCOCK ON THE VASCULAB 



[reb. 1, 



approximately oval in outline. It is prolonged forward to become 

 continuous with the outer coats of both precaval veins and the 

 aorta, and encloses within it the whole length of the pulmonary 

 artery. Behind, it is pierced close to the auricle by the postcaval 

 vein, so that this vessel has only a course 3 mm. in length within the 

 pericardium, in spite of the length of the intra-thoracic portion 

 of that vessel. Posteriorly, this layer is in contact with the dia- 

 phragm, but the connexion between them is of the slightest, the 

 most definite attachments being by means of the reilexion of the 

 pleura from the diaphragm on each side. 



Pig. 2. 



Heart and lungs of Pteropus mcdms, dorsal aspect. 

 Letters as in fig. 1. 



xU. 



Intimately connected with the libro-serous layer of the peri- 

 cardium is the so-called thymus gland, especially on the ventral 

 surface. Elsewhere this layer is thin and delicate, resembling the 

 human peritoneum in appearance, but firmer and less elastic than 

 that structure. 



The serous layer clothes the surface of the heart ; it is reflected 

 from the outer layer where the postcaval vein enters, as well as 

 at the entrance of the other vessels. 



