362 THE ANATOMY OF THE HOESE. 



Between the preceding two muscles a number of semi-iudependent 

 fleshy fasciculi connect adjacent coccygeal bones. Leyh describes these 

 separately as the intertransversales caudm. 



At the root of the tail, between the right and left depressors, the 

 retractor muscles of the penis take origin from the 1st and 2nd or 

 2nd and 3rd coccygeal bones ; and behind these the so-called suspensory 

 ligaments of the rectum are inserted (Plate 46). 



The Middle Coccygeal Artery (Plate 48). This is the largest 

 artery of the tail.* It is an unpaired vessel, and in the great majority 

 of cases it is a collateral branch detached from the inner side of the 

 lateral sacral artery towards the middle of the sacrum. Sometimes 

 it is detached in the same way from the left lateral sacral artery. 

 Passing backwards and inwards on the lower surface of the sacrum, it 

 places itself on the middle line, and extends in that position throughout 

 the tail, lying under the coccygeal vertebrae, and between the right 

 and left depressor muscles. In its backward course it gradually reduces 

 itself by giving off lateral branches. 



The Lateral Coccygeal Artery (Plate 48). Each artery (right or 

 left) is one of the terminal branches of the lateral sacral artery (the 

 ischiatic artery being the other branch). Having its origin towards the 

 middle of the sacrum, it passes backwards in the tail, crossing the sides 

 of the coccygeal bones, between the depressor and curvator muscles, the 

 former muscle separating it from the middle artery. It becomes smaller 

 by the detachment of numerous collateral twigs, the largest of which 

 pass upwards. Leyh designates this vessel the infero-lateral coccygeal 

 artery, describing as the supero-lateral coccygeal artery what is, 

 apparently, an unusually large branch of the first. 



Veins. The foregoing arteries are accompanied by veins of the same 

 names. 



Coccygeal Nerves. There are five or six pairs of coccygeal nerves, 

 and they are numbered according to the bones behind which they turn 

 outwards, the first issuing behind the first coccygeal vertebra, and so on 

 with the others. The first of them has a loop of communication with 

 the last sacral. As they turn outwards, they divide into an upper and 

 a lower branch corresponding to the superior and inferior primary 

 branches of the spinal nerves in other regions. The branches of each 

 of these sets are directed backwards, detaching slender filaments, and 

 then applying themselves to the next nerve of the same set. In this 

 way there are formed in each half of the tail two composite nerves, one of 

 which accompanies the lateral artery, while the other runs on the upper 

 aspect of the tail between the erector and curvator coccygis. These 

 cords are expended in branches to the muscles and skin of the tail. 



* Leyh describes and figures this artery as being smaller than the lateral coccygeal, 

 but that, certainly, is not usually the case. 



