SKELETON. 



673 



observed to occupy the interval between (c, d) 

 the ischiadic and pubic bones, and (3, 4, 5) 

 the sacral vertebrae. The junction between 

 the ilium and the sacral vertebras is called 

 sacro-iliac, whereas by the union of the ilium 

 (h,h) with the pubic and ischiadic bones (d,e), 

 the articular cup called acetabulum (g) is 

 formed. While the ilium becomes thus inter- 

 calated between the pubic and ischiadic bones 

 on the one hand, and the vertebra? on the 

 other, it severs the former from connection 

 with those vertebrae to which, as costse, they 

 properly belong ; and it obliterates that costal 

 quantity indicated in dotted outline at 3, 4-, 5, 

 which quantity, if it still persisted, would 

 unite the pubis and ischium to their proper 

 vertebrae. In fig. 491. I have represented in 

 A some of those lineae transversae (a, b, c), 

 which sketch out the form of the original 

 ventral ribs proper to the lumbar vertebras ; 

 and it will be seen that a, b, c hold series 

 with (d) the pubic bone, and (e) the ischiadic 

 bone. Between a, b, c, as the ventral ribs, 

 occur the intercostal spaces (//), and be- 

 tween the pubic and ischiadic bones (rf, e) 

 occurs that space (/) which, in human ana- 

 tomy, is named " thyroid foramen." Is not 

 this thyroid foramen an intercostal space, if 

 d ande becostae proper to the sacral vertebrae? 

 And do not the pubic and ischiadic sym- 

 phises at the point k correspond to the linea 

 alba (/, /), which stretches between the pubis 

 and sternum? 



In fig- B. we find the scapula (k, k, h, i) oc- 

 cupying, at this region of series, a position 

 similar to that which the iliac bone holds 

 elsewhere. But beneath the scapula the ribs 

 (2, 3, 4), for obvious purposes, persist ; while 

 beneath the iliac bone they are wanting. This 

 want of the ribs beneath the iliac bone, and 

 this presence of the ribs beneath the scapula, 

 constitute the difference. 



If those portions of the ribs (b and c of 

 jig. B.) which lie beneath the scapula suffered 

 metamorphosis, then b and c would abut upon 

 the glenoid cavity h, and would be to the 

 scapula what the pubic and ischiadic costiform 

 bones are to the ilium ; and then we should 

 have, between b and c of Jig. B., the inter- 

 costal space/ as corresponding to the thyroid 

 aperture. It is the costiform clavicle (a of B) 

 which becomes severed by the scapula from 

 its vertebra behind, just as the costiform os 

 pubis is severed by the iliac bone from its ver- 

 tebral quantity. 



The cotyloid cavity (g of A) is formed by 

 the junction of three bones, viz. the ilium 

 (A h}, the os pubis (d), and the ischium (e) ; 

 but it is the iliac facet of the cotyloid cavity 

 which alone corresponds to the glenoid cavity 

 of the scapula. If the ribs (b or c of fig. B.) 

 happened to be dissevered from their vertebrae 

 behind by an interval equal to the size of the 

 scapula (k, k, h), and if these sternal ends of 

 the ribs (b, c) then joined themselves to the 

 glenoid articular surface (h} of the scapula, 

 the three bones (h, b, and c) would also form 

 a cotyloid cavity for the head of the humerus. 



In those animals (birds, reptiles, &c.), where 



VOL. IV. 



two clavicles are required to be metamor- 

 phosed from ribs, they illustrate still further 

 the structural analogy which exists between 

 them and the ischiadic and pubic bones, which 

 latter exhibit, in relation to the ilium, the 

 same character that the clavicles manifest in 

 relation to the scapula. 



In fig' A. the os penis (/*) will be seen to 

 fall behind the symphisis pubis, while in fig. B. 

 the episternal ossicles (/*) will be noticed as 

 producing the sternal median line forwards 

 into the neck. At the subpubic region, where 

 t* occurs, and at the episternal region, where 

 the episternal ossicles occasionally appear, the 

 sternal median line is bounded in the animal ; 

 but in the comparative abstract animal, these 

 points may be regarded as unfinished. 



PROP. XL IV. The cranio-facial apparatus 

 of segments are proportionals of the dorso-ventral 

 archetypes. If it be true that the vertebral 

 quantity is a proportional of the sterno-costo- 

 vertebral quantity, and this latter a propor- 

 tional of the dorso-ventral archetype, then it 

 must follow that the cranio-facial apparatus, 

 which appears to bear a structural homology 

 with the sterno-costo-vertebral quantities, is 

 also constituted of segments which, like these 

 latter, are proportionals of the archetypal 

 quantities. Even though the whole animal 

 kingdom did not present us with a skeletal 

 form, upon whose cranium the dorsal rays 

 persisted complete, still the above-mentioned 

 inference may be legitimately drawn ; but 

 when, amongst the class of osseous fishes, we 

 find fig. 492., upon whose cranium the dor- 

 sal rays actually persist, then the d priori and 

 the d posteriori trains of reasoning meet and 

 answer to each other, while standing in pre- 

 sence of the fact itself, as nature produces it. 



In fig. 492. we see that the archetypal 

 dorso-ventral quantities (a, b, c, d) are conti- 

 nued into the head, not only by their centra, 

 their costal inferior arches, and their dorsal 

 laminas, which form the neural arches from 17 

 to 1, but also by their dorsal interspinous os- 

 sicles from m to n y and by their dorsal palms 

 from o to p. 



The head of the osseous fish (fig. 492.) of 

 the class Pleuronectidaj may be accounted, 

 therefore, as constituted of a series of the 

 dorso-ventral archetypes specially modified. 

 Between the cranial and the facial structures 

 is continued the line of spinal centra ; and 

 from these, as from the centra elsewhere 

 throughout spinal series, the dorsal and the 

 ventral rays project. The inferior cranial 

 rays are the jaw-bones (e f, h h) and hyoid 

 arches (g, g) ; the superior cranial rays are 

 the forms o p, m n. 



PROP. XLV. The cranio-facial apparatus is 

 the origin of the dorso-ventral archetypal series, 

 and the caudal apparatus is Us termination. 

 In the same animal, whose cranial structures 

 are still crested by the dorsal rays complete, 

 we find the opposite caudal extreme (/g.493.) 

 also crested by similar rays, dorsad as well as 

 ventrad. The spinal centra (n, m, I a) still 

 produce the entire rays (o, q) above and be- 

 low, while the terminal centrum (a) stands as 



x x 



