DEVELOPMENT OF THE SKULL IN THE PIG. 331 
of the incus (mediostapedial) ; the ascending part islargely fibrous (suprastapedial), and 
the part loosely attached to the mandibular arch is the elongated extrastapedial. ‘The 
short stylohyal afterwards coalesces with the body of the upper or incudal segment by 
an aftergrowth of cartilage (the “interhyal” tract); a long membranous space inter- 
venes between it and the glossal piece (ceratohyal). Thus the “columella” of the 
Bird is formed of three hyoidean and one periotic segment. 
In the Pig the hyoidean arch is distinct, but articulates closely with the mandibular ; 
its upper segment (hyomandibular) is converted into the incus, and becomes connected 
with the stapes, its disciform apex being ossified as the ‘os orbiculare.” ‘The stylo- 
hyal is dislocated and coalesces with the opisthotic region of the auditory capsule. 
The views which have hitherto been entertained respecting the mode of development 
of the ossicula auditus of the Mammalia fall under four heads:—- 
1. According to Retcuert*, the malleus and incus both result from the metamorphosis 
of the cartilaginous skeleton of the mandibular arch, while the stapes proceeds from an 
after segment of the hyoidean arch, which becomes separated and imbedded in the outer 
wall of the auditory capsule. 
The latest writer on the subject, SEMMER?, supports Reicuert’s views in the main, 
but is not quite sure about the origin of the stapes. 
2. GtytueRyT holds that not only the malleus and the incus, but the stapes as well, 
are the product of the metamorphosis of the skeleton of the mandibular arch. 
3. Maciror and Rosin 9, on the other hand, maintain that the malleus only takes its 
origin from the skeleton of the mandibular arch. ‘They consider the incus and stapes 
to arise independently, but do not expressly refer them to the skeleton of the second 
postoral visceral arch. 
4. Professor Huxtey||, arguing from the anatomy of the mandibular and hyoidean 
arches in the lower Vertebrata, has put forward the view that the malleus of the Mam- 
malia is the product of the metamorphosis of the proximal end of the cartilaginous 
skeleton of the mandibular arch, while the incus proceeds from the proximal end of the 
hyoidean arch, and is the homologue of the “ suprastapedial” of the Sawropsida. He 
expresses no opinion respecting the origin of the stapes. 
* « Ueber die Visceralbogen der Wirbelthiere,’ Mitier’s Archiv, 1837. 
y Untersuchungen iiber die Entwickelung der Meckel’schen Knorpels und seiner Nachbargebilde. Dorpat, 
1872. 
+ Beobachtungen tiber die Entwickelung des Gehérorganes bei Menschen und héheren Siiugethieren. Leipzig, 
1842. 
§ “ Mémoire sur un organe transitoire de la oie feetale désigné dans le nom cartilage de Mecxer,”’ Annales des 
Sciences Naturelles, s¢r. 4, i., xviii. 1862. 
|| “On the Representatives of the Malleus and the Incus of the Mammalia in the other Vertebrata,” Pro- 
ceedings of the Zoological Society, 1869. 
