ON THE VERTEBRATE SKELETON. 



333 



choice in the leg, for example, of the homotypes of the radius and ulna in 

 the fore-arm, is erroneous ; but the whole memoir is an admirable example 

 of the appreciation of correspondences which later researches in the same 

 direction have proved to flow from a higher and more general law of uni- 

 formity of type. It is, indeed, a striking instance of the secret but all-pre- 

 vailing harmony of the vertebrate structure that serial homologies should be 

 determinable to such an extent in the parts of the diverging appendages, 

 which are the seat of the greatest amount and variety of deviations from the 

 fundamental type. 



It will, of course, be obvious that the humerus is not 'the same bone' as 

 the femur of the same individual in the same sense in which the humerus 

 of one individual or species is said to be 'the same bone' as the humerus of 

 another individual or species. In the instance of serial homology above-cited, 

 the femur, though repeating in its segment the humerus in the more advanced 

 segment, is not its namesake, not properly, therefore, its ' homologue '. I 

 propose, therefore, to call the bones so related serially in the same skeleton 

 ' homotypes,' and to restrict the term ' homologue' to the corresponding bones 

 in different species, which bones bear, or ought to bear, the same names. 



In the skull those bones are homotypes, or repetitions of the same essential 

 part in the series of vertebral segments, which succeed each other length- 

 wise, as in the last four columns of the subjoined Table : — 



Vertebra. 



Centrums 



Neur apophyses 



Nasal spines 



Parapophyses 



Pleurapophyses 



Hcemapophyses 



Hcemal spines 



Diverging appendages 



Occipital. 



Basioccipital 



Exoccipital .... 

 Supraoccipital . . 

 Paroccipital .... 



Scapula 



Coracoid 



Epistemum .... 

 Fore-limb or fin 



Parietal. 



Basisphenoid. . . 

 Alisphenoid . . . 



Parietal 



Mastoid 



Stylohyal 



Ceratohyal 



Basihyal 



Branchiostegals 



Frontal. 



Presphenoid . . . 

 Orbitosphenoid 



Frontal , 



Postfrontal 



Tympanic 

 Articular 



Dentary , 



Operculum . . , 



Nasal. 



Vomer. 



Prefrontal. 



Nasal. 



None. 



Palatal. 



Maxillary. 



Premaxillary. 



Pterygoid and Zygoma. 



Thus the basioccipital, basisphenoid, presphenoid and vomer are homo- 

 types with the centrums of all the succeeding vertebras. The exoccipitals, 

 alisphenoids, orbitosphenoids, and prefrontals, are homotypes with the neur- 

 apophyses of all the succeeding vertebrae. The paroccipitals, mastoids and 

 postfrontals are homotypes with the transverse processes of all the succeeding 

 vertebrae. The supraoccipital, parietal, frontal and nasal are homotypes 

 with the vertebral neural spines. 



The petrosals, sclerotals, and turbinals are homotypes of each other, as 

 being respectively sense-capsules of the splanchno-skeleton. 



The suprascapula and scapula are together the homotypes of the stylohyal 

 and epihyal ; of the tympanic, whether simple or subdivided, and of the 

 palatal : and all these are the homotypes of the pleurapophyses collectively, 

 whether modified as ribs, hatchet-bones, or iliac bones, in the rest of the 

 vertebral segments. 



The coracoid is the homotype of the ceratohyal, this of the articular di- 

 vision of the mandible (with its subdivisions called angular, sur-angular and 

 coronoid, in cold-blooded animals), and this, again, of the maxillary bone : all 

 four being homotypes of the haemapophyses of the remaining vertebral seg- 

 ments, whether modified to form clavicles, pubic bones or ischia, chevron-bones, 

 sternal ribs, abdominal ribs, cartilages of ribs, abdominal cartilages or tendi- 

 nous intersections of the modified intercostal muscles called 'recti abdominis.' 



The entosternal, when present, is the homotype of the basihyal, of the 

 dentary or premandibular, and of the premaxillary bones ; and these collec- 

 tively are homotypes of the haemal spines of the rest of the vertebral seg- 



