on some fossil remains of man-第7章

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Mr。　　Busk's　'Crania　typica；'　have　a　very　different；　greatly　elongated
form；　and　may　be　termed　'oblong。'　　In　this　skull　the　extreme　length　is
to　the　extreme　breadth　as　100　to　not　more　than　67；　and　the　transverse
diameter　of　the　human　skull　may　fall　below　even　this　proportion。
People　having　such　skulls　were　called　by　Retzius　'dolichocephalic。'

　　　　＇footnote＇　*In　no　normal　human　skull　does　the　breadth　of　the
　　　　brain…case　exceed　its　length。

The　most　cursory　glance　at　the　side　views　of　these　two　skulls　will
suffice　to　prove　that　they　differ；　in　another　respect；　to　a　very
striking　extent。　　The　profile　of　the　face　of　the　Calmuck　is　almost
vertical；　the　facial　bones　being　thrown　downwards　and　under　the　forepart
of　the　skull。　The　profile　of　the　face　of　the　Negro；　on　the　other　hand；
is　singularly　inclined；　the　front　part　of　the　jaws　projecting　far
forward　beyond　the　level　of　the　fore　part　of　the　skull。　　In　the　former
case　the　skull　is　said　to　be　'orthognathous'　or　straight…jawed；　in　the
latter；　it　is　called　'prognathous；'　a　term　which　has　been　rendered；
with　more　force　than　elegance；　by　the　Saxon　equivalent；'snouty。'

Various　methods　have　been　devised　in　order　to　express　with　some　accuracy
the　degree　of　prognathism　or　orthognathism　of　any　given　skull；　most　of
these　methods　being　essentially　modifications　of　that　devised　by　Peter
Camper；　in　order　to　attain　what　he　called　the　'facial　angle。'

But　a　little　consideration　will　show　that　any　'facial　angle'　that　has
been　devised；　can　be　competent　to　express　the　structural　modifications
involved　in　prognathism　and　orthognathism；　only　in　a　rough　and　general
sort　of　way。　　For　the　lines；　the　intersection　of　which　forms　the　facial
angle；　are　drawn　through　points　of　the　skull；　the　position　of　each　of
which　is　modified　by　a　number　of　circumstances；　so　that　the　angle
obtained　is　a　complex　resultant　of　all　these　circumstances；　and　is　not
the　expression　of　any　one　definite　organic　relation　of　the　parts　of　the
skull。

FIG。　26。Side　and　front　views　of　the　round　and　orthognathous　skull　of　a
Calmuck；　after　Von　Baer。　　One…third　the　natural　size。

I　have　arrived　at　the　conviction　that　no　comparison　of　crania　is　worth
very　much；　that　is　not　founded　upon　the　establishment　of　a　relatively
fixed　base　line；　to　which　the　measurements；　in　all　cases；　must　be
referred。　　Nor　do　I　think　it　is　a　very　difficult　matter　to　decide　what
that　base　line　should　be。　　The　parts　of　the　skull；　like　those　of　the
rest　of　the　animal　framework；　are　developed　in　succession　the　base　of
the　skull　is　formed　before　its　sides　and　roof；　it　is　converted　into
cartilage　earlier　and　more　completely　than　the　sides　and　roof：　　and　the
cartilaginous　base　ossifies；　and　becomes　soldered　into　one　piece　long
before　the　roof。　　I　conceive　then　that　the　base　of　the　skull　may　be
demonstrated　developmentally　to　be　its　relatively　fixed　part；　the　roof
and　sides　being　relatively　moveable。

Fig。　27。Oblong　and　prognathous　skull　of　a　Negro；　side　and　front　views。
One…third　of　the　natural　size。

The　same　truth　is　exemplified　by　the　study　of　the　modifications　which
the　skull　undergoes　in　ascending　from　the　lower　animals　up　to　man。

FIG。　28。Longitudinal　and　vertical　sections　of　the　skulls　of　a　Beaver
（'Castor　Canadensis'）；　a　Lemur　（'L。　Catia'）；　and　a　Baboon
（'Cynocephalus　Papio'）；　'a　b'；　the　basicranial　axis；　'b　c'；　the
occipital　plane；　'i　T'；　the　tentorial　plane；　'a　d'；　the　olfactory　plane；
'f　e'；　the　basifacial　axis；　'c　b　a'；　occipital　angle；　'T　i　a'；
tentorial　angle；　'd　a　b'；　olfactory　angle；　'e　f　b'；　cranio…facial　angle；
'g　h'；　extreme　length　of　the　cavity　which　lodges　the　cerebral
hemispheres　or　'cerebral　length。'　　The　length　of　the　basicranial　axis
as　to　this　length；　or；　in　other　words；　the　proportional　length　of　the
line　'g　h'　to　that　of　'a　b'　taken　as　100；　in　the　three　skulls；　is　as
follows：Beaver　70　to　100；　Lemur　119　to　100；　Baboon　144　to　100。　　In　an
adult　male　Gorilla　the　cerebral　length　is　as　170　to　the　basicranial
axis　taken　as　100；　in　the　Negro　（Fig。　29）　as　236　to　100。　　In　the
Constantinople　skull　（Fig。　29）　as　266　to　100。　　The　cranial　difference
between　the　highest　Ape's　skull　and　the　lowest　Man's　is　therefore　very
strikingly　brought　out　by　these　measurements。　　In　the　diagram　of　the
Baboon's　skull　the　dotted　lines　'd1　d2'；　etc。；　give　the　angles　of　the
Lemur's　and　Beaver's　skull；　as　laid　down　upon　the　basicranial　axis　of
the　Baboon。　　The　line　'a　b'　has　the　same　length　in　each　diagram。

In　such　a　mammal　as　a　Beaver　（Fig。　28）；　a　line　（'a　b'。）　drawn　through
the　bones；　termed　basioccipital；　basisphenoid；　and　presphenoid；　is　very
long　in　proportion　to　the　extreme　length　of　the　cavity　which　contains
the　cerebral　hemispheres　（'g　h'。）。　　The　plane　of　the　occipital　foramen
（'b　c'。）　forms　a　slightly　acute　angle　with　this　'basicranial　axis；'
while　the　plane　of　the　tentorium　（'i　T'。）　is　inclined　at　rather　more
than　90　degrees　to　the　'basicranial　axis'；　and　so　is　the　plane　of　the
perforated　plate　（'a　d'。）；　by　which　the　filaments　of　the　olfactory　nerve
leave　the　skull。　　Again；　a　line　drawn　through　the　axis　of　the　face；
between　the　bones　called　ethmoid　and　vomerthe　〃basifacial　axis〃　（'f
e'。）　forms　an　exceedingly　obtuse　angle；　where；　when　produced；　it　cuts
the　'basicranial　axis。'

If　the　angle　made　by　the　line　'b　c'。　with　'a　b'。；　be　called　the
'occipital　angle；'　and　the　angle　made　by　the　line　'a　d'。　with　'a　b'。　be
termed　the　'olfactory　angle；'　and　that　made　by　'i　T'。　with　'a　b'。　the
'tentorial　angle；'　then　all　these；　in　the　mammal　in　question；　are　nearly
right　angles；　varying　between　80　degrees　and　110　degrees。　　the　angle　'e
f　b'。；　or　that　made　by　the　cranial　with　the　facial　axis；　and　which　may
be　termed　the　'cranio…facial　angle；'　is　extremely　obtuse；　amounting；　in
the　case　of　the　Beaver；　to　at　least　150　degrees。

But　if　a　series　of　sections　of　mammalian　skulls；　intermediate　between　a
Rodent　and　a　Man　（Fig。　28）；　be　examined；　it　will　be　found　that　in　the
higher　crania　the　basicranial　axis　becomes　shorter　relatively　to　the
cerebral　length；　that　the　'olfactory　angle'　and　'occipital　angle'
become　more　obtuse；　and　that　the　'cranio…facial　angle'　becomes　more
acute　by　the　bending　down；　as　it　were；　of　the　facial　axis　upon　the
cranial　axis。　　At　the　same　time；　the　roof　of　the　cranium　becomes　more
and　more　arched；　to　allow　of　the　increasing　height　of　the　cerebral
hemispheres；　which　is　eminently　characteristic　of　man；　as　well　as　of
that　backward　extension；　beyond　the　cerebellum；　which　reaches　its
maximum　in　the　South　America　Monkeys。　　So　that；　at　last；　in　the　human
skull　（Fig。　29）；　the　cerebral　length　is　between　twice　and　thrice　as
great　as　the　length　of　the　basicranial　axis；　the　olfactory　plane　is　20
degrees　or　30　degrees　on　the　'under'　side　of　that　axis；　the　occipital
angle；　instead　of　being　less　than　90　degrees；　is　as　much　as　150　degrees
or　160　degrees；　the　cranio…facial　angle　may　be　90　degrees　or　less；　and
the　vertical　height　of　the　skull　may　have　a　large　proportion　to　its
length。

It　will　be　obvious；　from　an　inspection　of　the　diagrams；　that　the
basicranial　axis　is；　in　the　ascending　series　of　Mammalia；　a　relatively
fixed　line；　on　which　the　bones　of　the　sides　and　roof　of　the　cranial
cavity；　and　of　the　face；　may　be　said　to　revolve　downwards　and　forwards
or　backwards；　according　to　their　position。　　The　arc　described　by　any
one　bone　or　plane；　however；　is　not　by　any　means　always　in　proportion　to
the　arc　described　by　another。

Now　comes　the　important　question；　can　we　discern；　between　the　lowest　and
the　highest　forms　of　the　human　cranium　anything　answering；　in　however
slight　a　degree；　to　this　revolution　of　the　side　and　roof　bones　of　the
skull　upon　the　basicranial　axis　observed　upon　so　great　a　scale　in　the
mammalian　series？　　Numerous　observations　lead　me　to　believe　that　we　must
answer　this　question　in　the　affirmative。

The　diagrams　in　Figure　29　are　reduced　from　very　carefully　made　diagrams
of　sections　of　four　skulls；　two　round　and　orthognathous；　two　long　and
prognathous；　taken　longitudinally　and　vertically；　through　the　middle。
The　sectional　diagrams　have　then　been　superimposed；　in　such　a　manner；
that　the　basal　axes　of　the　skulls　coincide　by　their　anterior　ends；