ay 
t 
. 
E. 
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. 
Tt 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 :— 
VERTEBRE. OcciPiTaAL. PaRIETAL. FRONTAL. NASAL. 
Centrums ..........++- Basioccipital ....|Basisphenoid...... Presphenoid ....|Vomer. 
Neurapophyses.... ..|Exoccipital ..../Alisphenoid ...... Orbitosphenoid. . |Prefrontal. 
Nasal spines..... ..|Supraoccipital ..|Parietal .......... Frontal ......., Nasal. 
Parapophyses ......:...|Paroccipital ....|Mastoid.......... Postfrontal...... None. 
Pleurapophyses ........ Seapula ........ Stylohyal ........ Tympanic ...... Palatal. 
Hemapophyses ........ Coracoid........ Ceratohyal........ Articular ...... Maxillary, 
Hemal spines .......... Episternum ....|Basihyal.......... Dentary ........ Premaxillary. 
Diverging appendages ..|Fore-limb or fin|Branchiostegals ..|Operculum ....|Pterygoidand Zygoma. 
Thus the basioccipital, basisphenoid, presphenoid and vomer are homo- 
types with the centrums of all the succeeding vertebra. The exoccipitals, 
alisphenoids, orbitosphenoids, and prefrontals, are homotypes with the neur- 
apophyses of all the succeeding vertebra. The paroccipitals, mastoids and 
postfrontals are homotypes with the transverse processes of all the succeeding 
vertebre. 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 heemapophyses 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 hemal spines of the rest of the vertebral seg- 
