120 



PELVIS. 



The COCCYX (fig. c), the hitckle, or whistle 

 bone (named from its supposed resemblance 

 to a cuckoo's bill, from KOKKV, Or.; Os coccygu, 

 Lat. ; rOs coccyx, Fr. ; das Steissbein, or 

 Schwanzbein, Germ.), is an appendage to the 

 apex of the sacrum, and terminates the spinal 

 column inferiorly. 



It forms the posterior boundary of the lower 

 part of the cavity, and inferior outlet of the 

 pelvis, assisting to complete its walls, to sustain 

 its contents, and to attach some muscles of the 

 leg and perineum. Its position is oblique 

 from behind, forwards and downwards, but 

 being normally movable on the sacrum, it 

 yields to pressure in both ways. It is usually 

 composed of four, rarely five pieces or tu- 

 bercles, which are generally, but not always, 

 soldered to each other, and diminished in size 

 and completeness downwards. When in one 

 piece, it presents a tapering, elongated, knob- 

 bed appearance with an anterior and posterior 

 surface, two lateral borders, and a base and 

 apex. The base presents a plane, oval, arti- 

 cular surface (#), corresponding to the apex 

 of the sacrum, with which it is articulated, 

 and sometimes ankylosed. Behind this, on 

 each side, projects upwards and backwards a 

 cornuated process (A), tipped with an ellip- 

 tical articular facet, directed upwards and 

 forwards, to articulate with the inferior sacral 

 horns. Below these, the borders commence, 

 presenting three alternate notches (<?), and 

 tubercular projections (e), of which the first 

 are much the largest, and complete the sacro- 

 coccygeal foramina. The borders are ter- 

 minated by a knobbed, sometimes bifurcated 

 apex, and give attachment to the sciatic liga- 

 ments, and some muscles (d). The first two 

 of these notches are converted into holes 

 by ligaments, for the passage of the posterior 

 branches of the fifth and sixth sacral nerves. 

 The anterior surface is slightly concave longi- 

 tudinally, and smooth, to support the rectum. 

 It has transverse markings, similar to the 

 sacrum. The posterior surface is correspond- 

 ingly converse and rough, to attach ligaments 

 and muscles. The internal structure of this 

 bone closely resembles that of the sacrum. 



DEVELOPEMENT. The innominate bone is 

 developed by three primitive and Jive com- 

 plementary points of ossification. 



The three primitive points commence in 

 the three component parts of the bone, the 

 ilium, ischium, and pubis respectively, from a 

 single piece of cartilage of the general form of 

 the bone. That of the ilium is placed in the 

 thick, arched rib above the cotyloid cavity, 

 (Jig. 79. A, a), being apparent, according to 

 Cruveilhier, the first in order, about the 

 fiftieth day of foetal life. BischofF, however, 

 says that the time of its appearance varies 

 from the second to the fourth month, in dif- 

 ferent individuals. About the fifth month, it 

 acquires somewhat of the form of the com- 

 plete bone. That of the ischium is placed in 

 the upper part of the descending ramns (6), 

 and appears second in order of time, always 

 later than the ilium, about the end of the third 

 month, or, according to BischofF, the fifth 



month. That of the pubis appears in the 

 superior branch, near the ilio-pectineal 

 eminence (c), at the end of the fifth month. 

 Bischoff fixes it later than Cruveilhier, at the 

 sixth or seventh month. At the period of 

 birth, the cotyloid cavity is still principally 

 cartilaginous (e), the ascending branch of the 

 ischium, the descending of the pubis, and 

 nearly the whole circumference of the ilium, 

 still remaining in the same condition (d). 



At the age of six or seven years, the branches 

 of the ischium and pubis are united by bone. 

 About the time of puberty, as first pointed 

 out by M. Serres, a distinct complementary 

 point of ossification appears in the cartilage 

 dividing the bones in the cotyloid cavity, 

 which soon including the whole of the Y-- 

 shaped cartilage at this part, and assuming 

 its shape and serrated margins, finally unites 

 them in the raised line before described. 

 According to Meckel, the pubis and ischium 

 join first with each other, and the ilium 

 becomes united to them afterwards. At 

 the same time appear the four remaining com- 

 plementary points as epiphyses, in the fol- 

 lowing order : namely, 1. On the whole length 

 of the iliac crest ; 2. At the anterior inferior 

 spine, not constant, and said to be more fre- 

 quent in the male than the female ; 3. Along 

 the whole extent of the tuberosity of the 

 ischium ; 4. On the symphysiul surface of the 

 pubis, said by Beclard to be more often found 

 in the female. All these are soldered .to the 

 bone, about the twenty-fourth or twenty-fifth 

 year, the epiphysis of the iliac crest being 

 the last to join. 



Fig. 79. 



Development of the lones of the human pelvis. (After 

 Quain and Sharpey.} 



A. Innominate bone of a full-grown foetus; a, 

 primary ossific point of ilium ; b, do. of ischium ; 

 c, do. of pubis ; d, d, cartilage ; e, Y-shaped cen- 

 tral cartilage. 



B, sacrum and coccyx at birth ; a, central ossific 

 points ; b, characteristic sacral do. ; c, coccyx still 

 cartilaginous. 



The sacrum is produced by the soldering 

 together of five vertebrae. Hence they have 

 been called the false or sacral vertebrcs. Oc- 

 casionally six pieces have been found, and, 

 more rarely, according to Soemmerring, four 

 pieces only are present. Each of these five 

 pieces, as in the other vertebras, results from 

 three primary points of ossification, viz., 

 one for each body or central portion, and 

 two for the posterior lateral surfaces and 

 laminae of each vertebra. These appear later 



