Mr. W. K. Parker on the Skull of the Pig. 253 



4. In pigs of larger size the form aud proportions of the parts 

 of the cranium become greatly altered, and ossification takes place 

 on an extensive scale, but no new structure is added. 



5. It follows from these facts that the mammalian skull, in an 

 early embryonic condition, is strictly comparable with that of an 

 Osseous Fish, a Frog, or a Bird at a like period of development, 

 consisting as it does of 



(rt) A cartilaginous basicranial plate embracing the notochord, 

 and, like it, stopping behind the pituitary body. 



{h) Paired cartilaginous arches, of wliich two are praeoral, \\ hile 

 the rest are postoral. 



(c) A pair of cartilaginous auditory capsules. 



{d) A pair of cartilaginous nasal capusles. 



Further, that in the Mammal, as in the other Vertebrata the deve- 

 lopment of the skull of which has been examined, the basicranial 

 plate grows up as an arch o^er the occipital region of the skull, 

 and coalesces with the auditory capsules, laterally, to give rise to 

 the primordial skeleton of the occipital, periotic, and basisphenoidal 

 regions of the skull. The trabeculie become fused togethei', and, 

 uniting with the olfactory capsules, give rise to the praesphenoidal 

 and ethmoidal parts of the cranium ; and the moieties of the 

 skidJ thus resulting from the metamorphosis of totally different 

 morphological elements become united aud give rise to the pri- 

 mordial cranium. 



As in the Salmon and Fowl, the second pair of praeoral arches 

 give rise to the pterygo-palatine apparatus ; in the Frog this arch 

 is late in appearance, and is never distinct from the trabecular 

 and mandibular bars, serving as a conjugational band between them. 

 The mandibular arch, which in the Salmon becomes converted into 

 Meckel's cartilage, the os articulare, the os quadratum, and the 

 OS metapterygoideum, in the Frog into Meckel's cartilage and the 

 quadrate cartilage (which early becomes confluent with the periotic 

 capsule), in the Bird into Meckel's cartilage, the os articulare, and 

 the OS quadratum (which articulates movably with the periotic cap- 

 sule), in the Pig is metamorphosed into Meckel's cartilage and the 

 malleus, which is loosely connected with the tegmen tympani, an 

 outgrowth of the periotic capsule. 



Meckel's cartilage persists in the Fish and in the Amphibia, but 

 disappears early in the Bird, and still earlier in the Mammal. The 

 permanent ossifications of the mandible are all membrane-bones in 

 Fish, Frog, and Fowl, but in the Mammal (exceptionally) the 

 ramus has a cartilaginous foundation. The hyoidean becomes 

 closely united with the mandibular arch, aud then segmented, in 

 the Fish, into the hyo-mandibular, the stylo-hyal, cerato-hyal, and 

 hypohyal — the hyo-mandibular, or proximal segment, articulating 

 with the outer wall of the periotic, and many of the segments of 

 the arch becoming dislocated. 



In the Frog, the hyoid also becomes segmented, but only after 

 extensive coalescence with the uuuidibuhir arch. The proximal 

 segment becomes the suprastapedial (hyo-mandibular) with its ex- 

 Ann. & Mag.N. Hist. Scr. 4. Vol. xiii. 18 



