SUBJECT IMD EX — MORPHOLOGICAL SECTION 



591 



" What can be more natural then than . . . 

 to conceive the skull as a portion of the verte- 

 bral column still more altered than the sacrum 

 or the coccyx, whose vertebrse are modified in 

 correspondence with the expansion of the an- 

 terior end of the nervous centre." 



Precisely this conception arose in the 

 mind of the " fancifvJ philosopher " Oken 

 after observing the bleached skull of a 

 deer which he picked up one day in 1806 

 in the Harz forest. 



These views, published in 1806 but 

 chiefly expressed in lectures, met with 

 general acceptance (Bojanus, L. 1818.1, 

 .2). In 1820, the poet Goethe in his 

 " Morphologie " stated that, thirty years 

 previously, he had discovered this re- 

 lationship and the vertebral theory has 

 subsequently often been known as the 

 Goethe-Oken theory. Goethe's preten- 

 sions are effectually disposed of by Old- 

 field Thomas (Encyc. Brit., 11th ed., 

 1911, vol. 20, p. 56). 



Opinions difiered, however, as to the 

 number of hypothetical vertebrse; Goethe 

 declared six, Oken three and later four, 

 and this number was also accepted by 

 Rathke in 1839, by Owen (R. 1846.1), 

 Brueh (C. 1S62.1), and by others, the 

 highest number suggested being seven. 



The theorj-, which had much declined, 

 was again revived with vigor in 1848 by 

 Owen (R. 1848.1). 



In 1858, Huxley (T. H. Add. 1859.2) 

 delivered his famous Croonian lecture on 

 the vertebrate skull, in which he effec- 

 tually disposed of the Okenian views, as 

 applied to the segmentation of the bony 

 skull, with the concluding statement 

 (p. 433). 



" The perfectly ossified skull is divisible into 

 a series of segments, whose analogy with verte- 

 brae is closer the nearer they lie to the occipital 

 region; but the relation is an analogy and not 

 an affinity and these cephahc sclerotomes are 

 not vertebrae." 



Modern views 



In 1872, Gegenbaur (C. 1864.2, iii) 

 published his epoch-making work on the 

 Selachian skull. In this he transferred 

 the fundamental idea of segmentation to 

 the chondrocranium which although form- 

 ing a continuous structure in the adult 

 Selachian, exhibits, especially behind the 

 infundibulum, many signs of an original 

 metameric or segmental structure. Ge- 

 genbaur conceived of the skull as composed 

 of an anterior prevertebral region, chiefly 

 formed by a forward growth around the 

 nasal organs and including the ethmoid 

 region, and a posterior vertebral region 

 comprising the occipital, auditory, and 

 part of the orbital regions. This latter 

 region overlies the notochord, precisely 

 as does the vertebral column, and it 

 gives exit to the segmental nerves which 

 he considered spinal nerves. He believed 

 the fused vertebrse to number at least 

 nine, chiefly because of the visceral arches 

 (BogenbUdungen) which he interpreted 

 as ventral or hsemal arch formations, 

 serially homologous with ribs. 



Stohr (P. A. 1882.1; Zeita. Wiss. Zool., 

 1S79, vols. 33, 34) soon added the fruitful 

 idea that the fusion of vertebrse had 

 progressed from front to rear; that this 

 caudal progression is still continuing; 

 and that it had proceeded unequally in 

 different groups, the skull of some forms 

 having absorbed more vertebrae than that 

 of others. 



This last idea has become further ex- 

 tended through the researcjies of Rosen- 

 berg (E. W. 1884.1, 1887.1), of Gegenbaur 

 (C. 1SS7.1), and of Sagemehl (M. 1884.1). 

 Rosenberg concladed that the correct 

 conception of the Selachian skull is not 

 that of a fixed size but that, for example, 

 the cranium of Carcharias includes one 

 vertebra more than that of Mustelus. 

 Sagemehl going still farther, believed 

 that, in mode of origin, the skull may be 

 divided into (1) the protomeiameric type, 

 found in Selachians and Amphibia, which 

 is formed by the fusion, not of vertebrae, 

 but of metameres or somites and (2) the 

 auximetameric type of Teleostomes and 

 Amniotes, in which the three anterior 

 vertebrae of the vertebral column, having 

 lost their freedom of motion through the 

 backward projection of the parasphenoid, 

 have been incorporated into the cranium. 

 With these views, however, Gegenbaur is 

 not in agreement. 



Various papers on the morphology of the 

 occipital region of the skull with especial 

 reference to the vertebral theory, Bertini, 

 E. 1907.1; Braohet, A. 1909.1; •Broh- 

 mer, P. 1909.1; Driiner, L. 1905.1; 

 Froriep, A. 1905.1, .3; *Gegen'baur, C. 

 1871.1, 1887.1, 1888.1, 1912.2; Nus- 

 baum, J. 1908.1; Rohon, J. V. 1894.1, 

 1895.2; Wijhe, J. W. Add. 1889.1. 



For the coalescence of vertebrce with the 

 occipital region of the skull in various 

 families of Ostariophysi (particularly Cy- 

 prinidcE and Siluridce) in connection with 

 the development and morphology of the We- 

 berian apparatus, see that topic under 

 Auditory Organs. 



Development of the skull 



"It has now been conclusively shown" 

 (quotingfromGoodrich, E. S. 1900.1,p. 11) . . . 

 " that skeletal segments of vertebral nature do, 

 in the course of ontogeny, and doubtless also in 

 that of phytogeny, become embodied^ in the 

 occipital region carrying with them their corre- 

 sponding nerves. Originally spinal nerves thus 

 come to pass through the cranial wall — so 

 called spino-occipitals." 



" This gradual inclusion of skeletal 

 segments, scleromeres, in the occipital 

 region of the skull of fish has lately been 

 followed in great detail from embryo to 

 adult by [our citations] -A-Severtzov, 

 A. N. 1895.1, 1897.1; Hoffman, C. K. 

 1894.1, 1896.1; Braus, H. 1899.1; and 

 Schreiner, K. E. 1902.1." 



For the intimately related topic of the 

 segmentation of the head, see Metamerism 

 under Head. 



Papers treating primarily of the chon- 

 drocranium of fishes. Filatoff, D. 1906.1; 

 Gegenbaur, C. 1867.2; Veit, 0. 1907.1, 



