VESTIGIAL PARTS. 65 
with the absence of the right jugular vein and carotid 
artery in many birds. This was attributed by Owen to 
the habit of birds sleeping with the head under the 
wing. This view is not supported by facts. 
Man, in common with the four anthropomorphous 
apes, has attached to the lower end of the cecum a 
small thin tube, which may vary from two to eight 
inches in length, known as the vermiform appendix 
(fig. 33). This tube agrees in structure with the rest 
of the intestine, is covered with peritoneum, possesses 
a muscular coat, and is lined with mucous membrane. 
In the early embryo it is equal in calibre to the rest of 
the bowel, but at a certain date it ceases to grow pari 
passu with it, and at the time of birth appears as a thin 
tubular appendix to the cecum. In the newly-born 
child it is often absolutely as long as in the full-grown 
man. This precocity is always an indication that the 
part was of great importance to the ancestors of the 
human species. 
Many mammals, closely allied to the anthropomor- 
phous apes, possess very large ceca; and in some of 
these the terminal segment of the cecum, although not 
represented as a thin, narrow tube, nevertheless resembles 
the vermiform appendix in that it possesses a very large 
proportion of the peculiar kind of tissue known as ade- 
noid, or lymphatic. 
In man the vermiform appendix is a typical example 
of a functionless part, and, like an idle person in a 
community, is not infrequently a source of considerable 
danger and suffering, and is responsible for a number 
of deaths annually. The danger may arise in three 
6 
