DISSECTION OF THE PELVIS. 375 



coccygeal vertebrae, while the outer portion extends to the extremity 

 of the tail, and is provided with strong tendons of insertion. 



Action. — It inclines the tail laterally or depresses it, according as 

 it acts alone or with the opposite muscle. 



Between the preceding two muscles a number of semi-independent 

 fleshy fasciculi connect adjacent coccygeal bones. Leyh describes these 

 separately as the intertransversales caudce. 



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 superolateral 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 com- 

 munication 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, 



